Rare earth magnet having high strength and high electrical resistance

ABSTRACT

This rare earth magnet having high strength and high electrical resistance has a structure including an R—Fe—B-based rare earth magnet particles  18  which are enclosed with a high strength and high electrical resistance composite layer  12 . The high strength and high electrical resistance composite layer  12  is constituted from a glass-based layer  16  that has a structure comprising a glass phase or R oxide particles  13  dispersed in glass phase, and R oxide particle-based mixture layers  17  that are formed on both sides of the glass-based layer  16  and contain an R-rich alloy phase  14  which contains  50  atomic % or more of R in the grain boundary of the R oxide particles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a rare earth magnet having high strength and high electrical resistance.

Priority is claimed on Japanese Patent Application Nos. 2005-170475, filed on Jun. 10, 2005, 2005-170476, filed on Jun. 10, 2005, and 2005-170477, filed on Jun. 10, 2005, the contents of which are incorporated herein by reference.

2. Description of Related Art

An R—Fe—B-based rare earth magnet, where R represents one or more kind of rare earth element including Y (this applies throughout this application), is known to have such a composition that contains R, Fe and B as basic components with Co and/or M (M represents one or more kind selected from among Ga, Zr, Nb, Mo, Hf, Ta, W, Ni, Al, Ti, V, Cu, Cr, Ge, C and Si; this applies throughout this application) added as required, specifically, 5 to 20% of R, 0 to 50% of Co, 3 to 20% of B and 0 to 5% of M are contained (% refers to atomic %, which applies throughout this application), with the balance consisting of Fe and inevitable impurities.

It is known that the R—Fe—B-based rare earth magnet can be manufactured by subjecting an R—Fe—B-based Tare earth magnet powder to hot pressing, hot isostatic pressing or the like. One of methods of manufacturing the R—Fe—B-based rare earth magnet powder is such that an R—Fe—B-based rare earth magnet alloy material that has been subjected to hydrogen absorption treatment is heated to a temperature in a range from 500 to 1000° C. and kept at this temperature in hydrogen atmosphere of pressure from 10 to 1000 kPa so as to carry out hydrogen absorption and decomposition treatment in which the R—Fe—B-based rare earth magnet alloy material is caused to absorb hydrogen and decompose through phase transition, followed by dehydrogenation of the R—Fe—B-based rare earth magnet alloy material by holding the R—Fe—B-based rare earth magnet alloy material in vacuum at a temperature in a range from 500 to 1000° C. It is known that the R—Fe—B-based rare earth magnet powder thus obtained has recrystallization texture consisting of adjoining recrystallized grains that are constituted from R₂Fe₁₄B type intermetallic compound phase that has substantially tetragonal structure as the main phase, and the recrystallization texture has the fundamental structure of magnetically anisotropic HDDR magnetic powder in which the fundamental structure has such a constitution that 50% by volume or more of the recrystallized grains are those which have such a shape as the ratio b/a of the least grain size a and the largest grain size b of the recrystallized grains is less than 2, and average size of the recrystallized grains is in a range from 0.05 to 5 μm (Japanese Patent No. 2,376,642).

In recent years, automobiles are employing increasing numbers of electrically powered devices, while great efforts are being made in the development of electric vehicles. In line with these trends, research and development activities have been increasing for the development of compact and high performance electronic devices and motors based on permanent magnet, for onboard applications. Improvement in the performance of the compact and high performance electronic devices and motors based on permanent magnet inevitably requires it to use the R—Fe—B-based rare earth magnet that has high magnetic anisotropy. However, the ordinary R—Fe—B-based rare earth magnet is a metallic magnet and therefore has low electrical resistance which, when used in a motor, causes a large eddy current loss that decreases the efficiency of the motor through heat generation from the magnet and other factors. To avoid this problem, R—Fe—B-based rare earth magnets that have high electrical resistance have been developed. It has been proposed to make one of these R—Fe—B-based rare earth magnets that have high electrical resistance by forming an R oxide layer in the grain boundary of R—Fe—B-based rare earth magnet particles so that the R—Fe—B-based rare earth magnet particles are enclosed with the R oxide layer to make a structure (Japanese Unexamined Patent Application, First Publication No. 2004-31780 and Japanese Unexamined Patent Application, First Publication No. 2004-31781).

However, since the rare earth magnet of the prior art that has high electrical resistance has a structure such that the R oxide layer exists in the grain boundary of the R—Fe—B-based rare earth magnet particles, bonding strength between the R—Fe—B-based rare earth magnet particles is weak, and therefore, the rare earth magnet of the prior art that has high electrical resistance has the problem of insufficient mechanical strength.

SUMMARY OF THE INVENTION

With the background described above, the present inventors conducted a research to make a rare earth magnet that has further higher strength and higher electrical resistance, It was found that satisfactory magnetic anisotropy and coercivity comparable to those of the conventional rare earth magnet and further higher strength and higher electrical resistance can be achieved with a rare earth magnet that is formed by stacking a composite layer which has high strength and high electrical resistance (hereinafter referred to as high strength and high electrical resistance composite layer) and an R—Fe—B-based rare earth magnet layer, wherein the high strength and high electrical resistance composite layer comprises a glass-based layer having a glass phase or a structure of R oxide particles dispersed in glass phase, and an R oxide particle-based mixture layers that are formed on both sides of the glass-based layer and contain an R-rich alloy phase which contains 50 atomic % or more of R in the grain boundary of the R oxide particles.

The present invention is based on the results of the research described above, and is characterized as:

-   (1) a rare earth magnet having high strength and high electrical     resistance formed by stacking the high strength and high electrical     resistance composite layer and the R—Fe—B-based rare earth magnet     layer, wherein the high strength and high electrical resistance     composite layer comprises a glass-based layer having a glass phase     or a structure of R oxide particles dispersed in a glass phase, and     the R oxide particle-based mixture layers that are formed on both     sides of the glass-based layer and which contain an R-rich alloy     phase which contains 50 atomic % or more of R in the grain boundary     of the R oxide particles.

According to the above invention, the glass-based layer in the high strength and high electrical resistance composite layer improves the insulation performance and increases the strength of bonding with the K oxide particle-based mixture layer. In addition, the R oxide particle-based mixture layer prevents the R—Fe—B-based rare earth magnet layer and the glass-based layer from reacting with each other, so that the magnetic property is prevented from decreasing and bonding strength is increased thereby making rare earth magnet having high strength and high electrical resistance that is excellent also in magnetic property. Presence of the high strength and high electrical resistance composite layer enables the rare earth magnet having high strength and high electrical resistance of the present invention to greatly improve the electrical resistance inside of the magnet so as to reduce the eddy current generated therein and thereby suppress the heat generation from the magnet significantly.

The present invention may also have such a constitution as:

-   (2) the rare earth magnet having high strength and high electrical     resistance as described in (1), wherein the high strength and high     electrical resistance composite layer further comprises an R oxide     layer formed on the surface of the R oxide particle-based mixture     layer opposite to the surface thereof that makes contact with the     glass-based layer, -   (3) the rare earth magnet having high strength and high electrical     resistance as described in (1), wherein the R—Fe—B-based rare earth     magnet layer has a composition such as 5 to 20% of R and 3 to 20% of     B (hereinafter % refers to atomic %), with the balance consisting of     Fe and inevitable impurities, -   (4) the rare earth magnet having high strength and high electrical     resistance as described in (1), wherein the R—Fe—B-based rare earth     magnet layer has such a composition as 5 to 20% of R, 3 to 20% of B,     and 0.001 to 5% of M (M represents one or more selected from the     group consisting of Ga, Zr, Nb, Mo, Hf, Ta, W, Ni, Al, Ti, V, Cu,     Cr, Ge, C, and Si), with the balance consisting of Fe and inevitable     impurities, -   (5) the rare earth magnet having high strength and high electrical     resistance as described in (1), wherein the R—Fe—B-based rare earth     magnet layer has a composition such as 5 to 20% of R, 0.1 to 50% of     Co, and 3 to 20% of B, with the balance consisting of Fe and     inevitable impurities, -   (6) the rare earth magnet having high strength and high electrical     resistance as described in (1), wherein the R—Fe—B-based rare earth     magnet layer has a composition such as 5 to 20% of R, 0.1 to 50% of     Co, 3 to 20% of B, and 0.001 to 5% of M, with the balance consisting     of Fe and inevitable impurities, or -   (7) the R—Fe—B-based rare earth magnet having high strength and high     electrical resistance wherein the R—Fe—B-based rare earth magnet     layer as described in (1), (2), (3), (4), (5) or (6) is a     magnetically anisotropic HDDR magnetic layer having a     recrystallization texture comprising adjoining recrystallized grains     containing an R₂Fe₁₄B type intermetallic compound phase having a     substantially tetragonal structure as a main phase, while the     recrystallization texture has a fundamental structure having a     constitution such that 50% by volume or more of the recrystallized     grains have a shape such that a ratio b/a of the minimum grain size     a and the maximum grain size b of the recrystallized grain is less     than 2, and the average size of the recrystallized grains is in a     range from 0.05 to 5 μm.

The present inventors also conducted a research to make a rare earth magnet having further higher strength and higher electrical resistance. It was found that satisfactory magnetic anisotropy and coercivity comparable to those of the conventional rare earth magnet and further higher strength and higher electrical resistance can be achieved with a rare earth magnet that has a structure such that the R—Fe—B-based rare earth magnet particles are enclosed with the composite layer having high strength and high electrical resistance, wherein the high strength and high electrical resistance composite layer comprises a glass-based layer having a glass phase or a structure of R oxide particles dispersed in glass phase, and R oxide particle-based mixture layers that are formed on both sides of the glass-based layer and contain an R-rich alloy phase which contains 50 atomic % or more of R in the grain boundary of the R oxide particles.

The present invention is based on the results of the research described above, and is characterized as:

-   (8) a rare earth magnet having high strength and high electrical     resistance having a structure such that the R—Fe—B-based rare earth     magnet particles are enclosed within the high strength and high     electrical resistance composite layer, wherein the high strength and     high electrical resistance composite layer comprises a glass-based     layer having a glass phase or a structure of R oxide particles     dispersed in a glass phase, and R oxide particle-based mixture     layers that are formed on both sides of the glass-based layer and     which contain an R-rich alloy phase which containing 50 atomic % or     more of R in the grain boundary of the R oxide particles.

According to the present invention, the glass-based layer provided in the high strength and high electrical resistance composite layer firer improves the insulation performance and increases the strength of bonding with the R oxide particle-based mixture layer. In addition, the R oxide particle-based mixture layers prevent the R—Fe—B-based rare earth magnet particles and the glass-based layer from reacting with each other, so that the magnetic property is prevented from decreasing and bonding strength is increased, thereby making rare earth magnet having high strength and high electrical resistance that is excellent also in magnetic property. Presence of the high strength and high electrical resistance composite layer enables the rare earth magnet having high strength and high electrical resistance of the present invention to greatly improve the electrical resistance inside of the magnet so as reduce the eddy current generated therein and thereby suppress the heat generation from the magnet significantly.

The present invention may also have such a constitution as:

-   (9) the rare earth magnet having high strength and high electrical     resistance as described in (8), wherein the high strength and high     electrical resistance composite layer further comprises an R oxide     layer formed on the surface of the R oxide particle-based mixture     layer opposite to the surface thereof that makes contact with the     glass-based layer, -   (10) the rare earth magnet having high strength and high electrical     resistance as described in (8), wherein the R—Fe—B-based rare earth     magnet particles are particles of rare earth magnet that have a     composition such as 5 to 20% of R and 3 to 20% of B, with the     balance consisting of Fe and inevitable impurities, -   (11) the rare earth magnet having high strength and high electrical     resistance as described in (8), wherein the R—Fe—B-based rare earth     magnet particles are particles of rare earth magnet that have a     composition such as 5 to 20% of R, 3 to 20% of B, and 0.001 to 5% of     M, with the balance consisting of Fe and inevitable impurities, -   (12) the rare earth magnet having high strength and high electrical     resistance as described in (8), wherein the R—Fe—B-based rare earth     magnet particles are particles of rare earth magnet that have a     composition such as 5 to 20% of R, 0.1 to 50% of Co, and 3 to 20% of     B, with the balance consisting of Fe and inevitable impurities, -   (13) the rare earth magnet having high strength and high electrical     resistance as described in (8), wherein the R—Fe—B-based rare earth     magnet particles are particles of rare earth magnet that have a     composition such as 5 to 20% of R, 0.1 to 50% of Co, 3 to 20% of B,     and 0.001 to 5% of M, with the balance consisting of Fe and     inevitable impurities, or -   (14) the R—Fe—B-based rare earth magnet having high strength and     high electrical resistance, wherein the R—Fe—B-based rare earth     magnet particles as described in (8), (9), (10), (11), (12) or (13)     are particles of magnetically anisotropic HDDR magnet having a     recrystallization texture comprising adjoining recrystallized grains     contains R₂Fe₁₄B type intermetallic compound phase of substantially     tetragonal structure as the main phase, while the recrystallization     texture has a fundamental structure having such a constitution that     50% by volume or more of the recrystallized gains are those which     have such a shape as the ratio b/a of the least grain size a and the     largest grain size b of the recrystallized grains is less than 2,     and avenge size of the recrystallized grains is in a range from 0.05     to 5 μm.

The present inventors also conducted a research to make a rare earth magnet having further higher strength and higher electrical resistance. It was found that higher strength and higher electrical resistance than those of a conventional rare earth magnet of high electrical resistance, which have such a constitution as an R oxide layer is formed in the grain boundary of the R—Fe—B-based rare earth magnet particles so that the R—Fe—B-based rare earth magnet particles are enclosed with the R oxide layer, can be achieved with a rare earth magnet formed by stacking a composite layer having high strength and high electrical resistance hereinafter referred to as the high strength and high electrical resistance composite layer) constituted from two oxide layers of R (R represents one or more kind of rare earth elements including Y; this applies throughout this application) that sandwich one glass layer and an R—Fe—B-based rare earth magnet layer, wherein the high strength and high electrical resistance composite layer is provided between the R—Fe—B-based rare earth magnet layers.

The present invention is based on the results of the research described above, and is characterized as:

-   (15) a rare earth magnet having high strength and high electrical     resistance comprising: a high strength and high electrical     resistance composite layer that is formed by stacking R oxide layers     on both sides of a glass layer and an R—Fe—B-based rare earth magnet     layer to be stacked, wherein the high strength and high electrical     resistance composite layer is provided between the R—Fe—B-based rare     earth magnet layer.

According to the present invention, the glass layer provided in the high strength and high electrical resistance composite layer increases the bonding strength between the R oxide layers, thus resulting in higher mechanical strength of the rare earth magnet, higher insulation and high strength and high electrical resistance. In addition, presence of the high strength and high electrical resistance composite layer enables the rare earth magnet having high strength and high electrical resistance of the present invention to greatly improve the electrical resistance inside of the magnet so as reduce the eddy current generated therein and thereby suppress the heat generation from the magnet significantly.

The present invention may also have such a constitution as:

-   (16) the rare ea magnet having high strength and high electrical     resistance as described in (15) wherein the R—Fe—B-based rare earth     magnet layer has such a composition as 5 to 20% of R and 3 to 20% of     B are contained, with the balance consisting of Fe and inevitable     impurities, -   (17) the rare earth magnet having high strength and high electrical     resistance as described in (15) wherein the R—Fe—B-based rare earth     magnet layer has such a composition as 5 to 20% of R, 3 to 20% of B,     and 0.001 to 5% of M are contained, with the balance consisting of     Fe and inevitable impurities, -   (18) the rare earth magnet having high strength and high electrical     resistance as described in (15) wherein the R—Fe—B-based rare earth     magnet layer has such a composition as 5 to 20% of R, 0.1 to 50% of     Co, and 3 to 20% of B are contained, with the balance consisting of     Fe and inevitable impurities, -   (19) the rare earth magnet having high strength and high electrical     resistance as described in (15) wherein the R—Fe—B-based rare earth     magnet layer has such a composition as 5 to 20% of R, 0.1 to 50% of     Co, 3 to 20% of B, and 0.001 to 5% of M are contained, with the     balance consisting of Fe and inevitable impurities, or -   (20) the R—Fe—B-based rare earth magnet having high strength and     high electrical resistance wherein the R—Fe—B-based rare earth     magnet layer as described in (15), (16), (17), (18) or (19) is a     layer of magnetically anisotropic HDDR magnet having a     recrystallization texture comprising adjoining recrystallized grains     contains R₂Fe₁₄B type intermetallic compound phase of substantially     tetragonal structure as the main phase, while the recrystallization     texture has a fundamental structure having such a constitution that     50% by volume or more of the recrystallized grains are those which     have such a shape as the ratio b/a of the least grain size a and the     largest grain size b of the recrystallized grain is less than 2, and     average size of the recrystallized grains is in a range from 0.05 to     5 μm.

The present inventors further conducted a research to make a rare earth magnet having further higher strength and higher electrical resistance. It was found that satisfactory magnetic anisotropy and coercivity comparable to those of the conventional rare earth magnet and further higher strength and higher electrical resistance can be achieved with a rare earth magnet having a structure having the R—Fe—B-based rare earth magnet particles which are enclosed with the high strength and high electrical resistance composite layer formed by stacking the R oxide layers on both sides of the glass layer in contact therewith.

The present invention is based on the results of the research described above, and is characterized as:

-   (21) a rare earth magnet having high strength and high electrical     resistance having a structure such that the R—Fe—B-based rare earth     magnet particles are enclosed with a high strength and high     electrical resistance composite layer formed by stacking R oxide     layers on both sides of a glass layer in contact therewith.

The rare earth magnet having high strength and high electrical resistance of the present invention, comprises the R—Fe—B-based rare earth magnet particles and the high strength and high electrical resistance composite layer having the R oxide layer formed in the grain boundaries of the R—Fe—B-based rare earth magnet particles and the glass layer, in which the R—Fe—B-based rare earth magnet particles have a structure that are enclosed with the high strength and high electrical resistance composite layer that is provided in the grain boundary of the R—Fe—B-based rare earth magnet particles. Presence of the glass layer in the high strength and high electrical resistance composite layer enables bonding strength between the R oxide layer to increase, thus resulting in greatly increased mechanical strength of the rare earth magnet, higher insulation and high strength and high electrical resistance. In addition, presence of the high strength and high electrical resistance composite layer enables the rare earth magnet having high strength and high electrical resistance of the present invention to greatly improve the electrical resistance inside of the magnet so as reduce the eddy current generated therein and thereby suppress the heat generation from the magnet significantly.

The present invention may also have such a constitution as:

-   (22) the rare earth magnet having high strength and high electrical     resistance as described in (21) wherein the R—Fe—B-based rare earth     magnet particles have such a composition as 5 to 20% of R and 3 to     20% of B are contained, with the balance consisting of Fe and     inevitable impurities, -   (23) the rare earth magnet having high strength and high electrical     resistance as described in (21) wherein the R—Fe—B-based rare earth     magnet particles have such a composition as 5 to 20% of R, 3 to 20%     of B, and 0.001 to 5% of M are contained, with the balance     consisting of Fe and inevitable impurities, -   (24) the rare earth magnet having high strength and high electrical     resistance as described in (21) wherein the R—Fe—B-based rare earth     magnet particles have such a composition as 5 to 20% of R, 0.1 to     50% of Co, and 3 to 20% of B are contained, with the balance     consisting of Fe and inevitable impurities, -   (25) the rare earth magnet having high strength and high electrical     resistance as described in (21) wherein the R—Fe—B-based rare earth     magnet particles have such a composition as 5 to 20% of R, 0.1 to     50% of Co, 3 to 20% of B, and 0.001 to 5% of M are contained, with     the balance consisting of Fe and inevitable impurities, while -   (26) the R—Fe—B-based rare earth magnet having high strength and     high electrical resistance wherein the R—Fe—B-based rare earth     magnet particles as described in (21), (22), (23), (24) or (25) are     particles of magnetically anisotropic HDDR magnet having a     recrystallization texture comprising adjoining recrystallized grains     contains R₂Fe₁₄B type intermetallic compound phase of substantially     tetragonal structure as the main phase, while the recrystallization     texture has a fundamental structure having such a constitution that     50% by volume or more of the recrystallized as are those which have     such a shape as the ratio b/a of the least grain size a and the     largest grain size b of the recrystallized grain is less than 2, and     average size of the recrystallized grains is in a range from 0.05 to     5 μm.

The rare earth magnet having high strength and high electrical resistance of the present invention is capable of enduring severe vibration because of the high strength, and makes it possible to improve the performance of a permanent magnet motor that incorporates the rare earth magnet having high strength and high electrical resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the structure of a rare earth magnet of the present invention.

FIG. 2 is a schematic diagram showing the structure of a rare earth magnet of the present invention.

FIG. 3 is a schematic diagram showing the structure of a rare earth magnet of the present invention.

FIG. 4 is a schematic diagram showing the structure of a rare earth magnet of the present invention.

FIG. 5 is a schematic diagram showing the structure of a rare earth magnet of the present invention.

FIG. 6 is a schematic diagram showing the structure of a rare earth magnet of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The rare earth magnet having high strength and high electrical resistance of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing a cross section of the rare earth magnet having high strength and high electrical resistance described in (1). In FIG. 1, a rare earth magnet 1 comprises an R—Fe—B-based rare earth magnet layer 11, a high strength and high electrical resistance composite layer 12, R oxide particles 13, an R-rich alloy phase 14, a glass phase 15, a glass-based layer 16, and an R oxide particle-based mixture layer 17. The high strength and high electrical resistance composite layer 12 has a structure such that the R oxide particle-based mixture layers 17 are formed on both sides of the glass-based layer 16 in contact therewith, while the high strength and high electrical resistance composite layer 12 is provided between the R—Fe—B-based rare earth magnet layers 11. The glass-based layer 16 has a structure consisting of a glass phase only or the R oxide particles 13 dispersed in the glass phase 15, and the R oxide particle-based mixture layer 17 contains the R-rich alloy phase 14 which contains 50 atomic % or more of R in the grain boundary of the R oxide particles 13.

Because of such a stacking structure, the high strength and high electrical resistance composite layer 12 has further improved insulation property due to the glass-based layer 16 and increased bonding strength with the R oxide particle-based mixture layer 17. The R oxide particle-based mixture layer 17 prevents the R—Fe—B-based rare earth magnet layer 11 and the glass-based layer 16 from reacting with each other, prevents the magnetic property from decreasing and increases the bonding strength, thereby making the rare earth magnet having high strength and high electrical resistance that is excellent also in magnetic property. Presence of the high strength and high electrical resistance composite layer 12 enables the rare earth magnet 1 having high strength and high electrical resistance of the present invention to greatly improve the electrical resistance inside of the magnet 1 so as reduce the eddy current generated therein and thereby suppress the heat generation from the magnet significantly.

While the rare earth magnet having a constitution of one high strength and high electrical resistance composite layer 12 being provided between two R—Fe—B-based rare earth magnet layers 11 is shown in FIG. 1 to make the invention easier to understand, the rare earth magnet having high strength and high electrical resistance of the present invention may also have such a constitution as n pieces (n is a positive integer) of high strength and high electrical resistance composite layers 12 are provided between n+1 pieces of R—Fe—B-based rare earth magnet layers 11 alternately.

The high strength and high electrical resistance composite layer 12 may also have an R oxide layer formed on the surface of the R oxide particle-based mixture layer 17 opposite to the surface that makes contact with the glass-based layer 16.

FIG. 2 is a schematic sectional view of the rare earth magnet having high strength and high electrical resistance in the constitution that the high strength and high electrical resistance composite layer 12 has the R oxide layer, namely the rare earth magnet having high strength and high electrical resistance described in (2).

In FIG. 2, the rare earth magnet 2 comprises the R—Fe—B-based rare earth magnet layer 11, the high strength and high electrical resistance composite layer 12, the R oxide particles 13, the R-rich alloy phase 14, the glass phase 15, the glass-based layer 16, the R oxide particle-based mixture layer 17, and an R oxide layer 19.

As shown in FIG. 2, the high strength and high electrical resistance composite layer 12 has a structure such that the R oxide particle-based mixture layers 17 are stacked on both sides of the glass-based layer 16 in contact therewith, and has the R oxide layer 19 formed on the surface of the R oxide particle-based mixture layer 17 opposite to the surface thereof that makes contact with the glass-based layer 16, while the high strength and high electrical resistance composite layer 12 is provided between the R—Fe—B-based rare earth magnet layers 11.

The glass-based layer 16 has a structure consisting of glass phase only or the R oxide particles 13 dispersed in the glass phase 15, and the R oxide particle-based mixture layer 17 contains an R-rich alloy phase which contains 50 atomic % or more R in the grain boundary of the R oxide particles, and the R oxide layer 19 is composed of oxide of R.

Because of such a stacking structure, the high strength and high electrical resistance composite layer 12 has further improved insulation property due to the glass-based layer 16 and the R oxide layer 19 and increased bonding strength with the R oxide particle-based mixture layer 17. The R oxide particle-based mixture layer 17 and the R oxide layer 19 prevent the R—Fe—B-based rare earth magnet layer 11 and the glass-based layer 16 from reacting with each other, prevent the magnetic property from decreasing and increase the bonding strength. Presence of the high strength and high electrical resistance composite layer 12 increases the strength of entire magnet so as to be capable of enduring severe vibration, and enables the rare earth net to greatly improve the electrical resistance of the inside of the magnet so as to reduce the eddy current generated therein, and thereby suppress the heat generation from the magnet significantly, while providing excellent magnetic property.

While the rare earth magnet having a constitution of one high strength and high electrical resistance composite layer 12 being provided between two R—Fe—B-based rare earth magnet layers 11 is shown in FIG. 2 to make the invention easier to understand, the rare earth magnet having high strength and high electrical resistance of the present invention may have a constitution such that n pieces (n is a positive integer) of high strength and high electrical resistance composite layers 12 are provided between n+1 R—Fe—B-based rare earth magnet layers 11 alternately.

FIG. 3 is a schematic sectional view of the rare earth magnet having high strength and high electrical resistance described in (15). In FIG. 3, the rare earth magnet 3 comprises an R—Fe—B-based rare earth magnet layer 31, a high strength and high electrical resistance composite layer 32, an R oxide layer 33, and a glass layer 34. The high strength and high electrical resistance composite layer 32 has a structure such that the R oxide layers 3 are stacked on both sides of the glass layer 34 in contact therewith, and the high strength and high electrical resistance composite layer 32 is provided between the R—Fe—B-based rare earth magnet layers 31.

Because the high strength and high electrical resistance composite layer 32 has a stacking structure as described above, bonding between the R oxide layers 33 is made firmer by the glass layer 34 so that strength of the rare earth magnet is greatly improved while the insulation property is improved and high strength and high electrical resistance are achieved. Also the presence of the high strength and high electrical resistance composite layer 32 enables the rare earth magnet having high strength and high electrical resistance of the present invention to greatly improve the electrical resistance inside of the magnet so as to reduce the eddy current generated therein and thereby suppress the heat generation from the magnet significantly.

While the rare earth magnet having a constitution such that one high strength and high electrical resistance composite layer 32 is provided between two R—Fe—B-based rare earth magnet layers 31 in FIG. 3 to make the invention easier to understand, the rare earth magnet having high strength and high electrical resistance of the present invention may have a constitution such that n pieces (n is a positive integer) of high strength and high electrical resistance composite layer 32 are provided between n+1 R—Fe—B-based rare earth magnet layers 31 alternately.

The R—Fe—B-based rare earth magnet layers 11 and 31 may have a composition such that 5 to 20% of R and 3 to 20% of B are contained with the balance consisting of Fe and inevitable impurities, or a composition such that 5 to 20% of R, 3 to 20% of B, and 0.001 to 5% of M are contained with the balance consisting of Fe and inevitable impurities, or a composition such that 5 to 20% of R, 0.1 to 50% of Co, and 3 to 20% of B are contained with the balance consisting of Fe and inevitable impurities, or a composition such that 5 to 20% of R, 0.1 to 50% of Co, 3 to 20% of B, and 0.001 to 5% of M are contained with the balance consisting of Fe and inevitable impurities.

FIG. 1 shows the high strength and high electrical resistance composite layer 12 in a structure such that the R oxide particle-based mixture layers 17 are stacked on both sides of the glass-based layer 16 in contact therewith, and the high strength and high electrical resistance composite layer 12 is provided between the R—Fe—B-based rare earth magnet layers 11, 11. It is preferable that the glass-based layer 16 is formed by softening and fusing the glass powder to form a glass phase or causing the R oxide particles to disperse in the softened glass phase during formation by hot pressing, and the R oxide particle-based mixture layer 17 is formed by causing the R-rich alloy phase 14 containing 50 atomic % or more of R contained in the R—Fe—B-based rare earth magnet layer 11 to enter the grain boundary between the R oxide particles 13 during formation by hot pressing.

While R of the R oxide particles 13 that constitute the high strength and high electrical resistance composite layer 12 may or may not be the same R contained in the R—Fe—B-based rare earth magnet layer 11, it is preferably one or more kind selected from among Y, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and is more preferably Tb and/or Dy.

FIG. 2 shows the high strength and high electrical resistance composite layer 12 which is formed by stacking the R oxide particle-based mixture layers 17 on both sides of the glass-based layer 16 in contact therewith and further has the R oxide layer 19 formed on the surface of the R oxide particle-based mixture layer 17 opposite to the surface that makes contact with the glass-based layer 16, while the high strength and high electrical resistance composite layer 12 is provided between the R—Fe—B-based rare earth magnet layers 11, 11. It is preferable that the glass-based layer 16 is formed by softening and fusing the glass powder to form a glass phase or causing the R oxide particles to disperse in the softened glass phase during formation by hot pressing, and the R oxide particle-based mixture layer 17 is formed by causing the R-rich alloy phase 14 containing 50 atomic % or more of R contained in the R—Fe—B-based rare earth magnet layer 11, to enter the grain boundary of the R oxide particles 13 during formation by hot pressing.

Thus the R oxide particle-based mixture layer 17 is formed as the R-rich alloy phase 14 which contains 50 atomic % or more R contained in the R—Fe—B-based rare earth magnet layer 11 enters through a portion of the R oxide layer 19 where it is cracked or peeled off into the grain boundary of the R oxide particles 13 during formation by hot pressing or the like.

While R of the R oxide particles 13 and of the R oxide layer 19 that constitute the high strength and high electrical resistance composite layer 12 may or may not be the same R contained in the R—Fe—B-based rare earth magnet layer 11, it is preferably one or more kind selected from the group consisting of Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and is more preferably Tb and/or Dy. Also R of the R-rich alloy phase 14 is preferably the same as the R contained in the R—Fe—B-based rare earth magnet layer 11, but may be different from the R contained in the R—Fe—B-based rare earth magnet layer 11.

In FIG. 3, while R of the R oxide layer 33 that constitutes the high strength and high electrical resistance composite layer 32 may or may not be the same as the R contained in the R—Fe—B-based rare earth magnet layer 31, it is preferably one or more kind selected from among Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and is more preferably Tb and/or Dy.

The R—Fe—B-based rare earth magnet layers 11 and 31 are more preferably magnetically anisotropic HDDR magnetic layers having a recrystallization texture consisting of adjoining recrystallized grains that are constituted from an R₂Fe₁₄B type intermetallic compound phase of a substantially tetragonal structure as the main phase, while the recrystallization texture has a fundamental structure contain 50% by volume or more of the recrystallized grains having a shape such that the ratio b/a of the minimum grain size a and the maximum grain size b of the recrystallized grain is less than 2, and the average size of the recrystallized grains is in a range from 0.05 to 5 μm.

An example of manufacturing the rare earth magnet having high strength and high electrical resistance of the present invention shown in FIG. 1 is as follows.

An R—Fe—B-based rare earth magnet powder green compact layer is formed from an ordinary R—Fe—B-based rare earth magnet powder that has high magnetic anisotropy by a forming process in magnetic field. An R oxide particle slurry is applied onto the upper and lower surfaces or the upper surface of the R—Fe—B-based rare earth magnet powder green compact layer by spin coating method or the like so as to form an R oxide particle slurry layer. The R oxide particle slurry layer is then coated with a slurry of glass powder or a mixed powder, consisting of glass powder as the main component with the addition of R oxide powder (hereinafter referred to as glass-based powder), by spin coating method or the like so as to form a glass-based powder slurry layer. Another R—Fe—B-based rare earth magnet green compact layer prepared by coating the glass-based powder slurry layer with the R oxide particle slurry is provided to face the R oxide particle slurry layer, hereby to make a stacked green compact. By hot pressing this stacked green compact, the rare earth magnet having high strength and high electrical resistance of the present invention shown in FIG. 1 is obtained.

The hot-pressed material thus obtained is constituted from the high strength and high electrical resistance composite layer 12 and the R—Fe—B-based rare earth magnet layer 11 stacked one on another as shown in FIG. 1. The high strength and high electrical resistance composite layer 12 has a structure such that the R oxide particle-based mixture layers 17 are stacked on both sides of the glass-based layer 16 in contact therewith, where the glass-based layer 16 is formed by softening and fusing the glass powder to form glass phase or causing the R oxide particles to disperse in the softened glass phase during the hot pressing process, and the R oxide particle-based mixture layer 17 is formed by causing the R-rich alloy phase, which contains 50 atomic % or more of R contained in the R—Fe—B-based rare earth magnet layer 11, to enter the grain boundary of the R oxide particles during the hot pressing process.

An example of manufacturing the rare earth magnet having high strength and high electrical resistance of the present invention shown in FIG. 2 is as follows.

An R—Fe—B-based rare earth magnet powder green compact layer is formed from an ordinary R—Fe—B-based rare earth magnet powder that has high magnetic anisotropy by a forming process in magnetic field. A sputtered layer of R oxide is formed on the surface of the R—Fe—B-based rare earth magnet powder green compact layer, and the sputtered layer of R oxide is coated with an R oxide particle slurry by spin coating method or the like, which is then dried so as to form an R oxide particle slurry layer. The R oxide particle slurry layer is then coated with a slurry of glass powder so as to form a glass powder slurry layer. Another R—Fe—B-based rare earth magnet powder green compact layer prepared by coating the glass-based powder slurry layer with the R oxide particle slurry layer is provided to face the R oxide particle slurry layer, thereby to make a stacked green compact. By hot pressing this stacked green compact, the rare earth magnet having high strength and high electrical resistance of the present invention shown in FIG. 2 is obtained.

The hot-pressed material thus obtained is constituted from the high strength and high electrical resistance composite layer 12 and the R—Fe—B-based rare earth magnet layer 11 stacked one on another, similarly to the rare earth magnet having high strength and high electrical resistance shown in FIG. 1. The high strength and high electrical resistance composite layer 12 has a structure such that the R oxide particle-based mixture layers 17 are stacked on both sides of the glass-based layer 16 in contact therewith, where the glass-based layer 16 is formed by softening and Easing the glass powder to form the glass phase or causing the R oxide particles to disperse in the softened glass phase during the hot pressing process, and the R oxide particle-based mixture layer 17 is formed by causing the R-rich alloy phase, which contains 50 atomic % or more of R contained in the R—Fe—B-based rare earth magnet layer 11, to enter the grain boundary of the R oxide particles during the hot pressing process.

An example of manufacturing the rare earth magnet having high strength and high electrical resistance of the present invention shown in FIG. 3 as follows.

An R—Fe—B-based rare earth magnet powder green compact layer is formed from an ordinary R—Fe—B-based rare earth magnet powder that has high magnetic anisotropy by a forming process in magnetic field, A sputtered layer of oxide of rare earth element is formed on the upper and lower surfaces or the upper surface of the R—Fe—B-based rare earth magnet powder green compact layer, so as to make at least two stacked bodies constituted from the R—Fe—B-based rare earth magnet powder green compact layer and the R oxide layer. These stacked bodies are placed one on another so as to provide the glass powder layer between the K oxide layers, thereby to form a stacked green compact constituted from the R—Fe—B-based rare earth magnet powder green compact layer, the R oxide layer, the glass powder layer, the R oxide layer, and the R—Fe—B-based rare earth magnet powder green compact layer in order. By hot pressing this stacked green compact, the rare earth magnet having high strength and high electrical resistance of the present invention shown in FIG. 3 is obtained.

The hot-pressed material thus obtained is constituted from the R—Fe—B-based rare earth magnet layers 31 and the high strength and high electrical resistance composite layer 32 that comprises the R oxide layers 33, 33 and the glass layer 34 stacked one on another, as shown in FIG. 3. The high strength and high electrical resistance composite layer 32 has the structure of interposing the glass layer 34 by the R oxide layers 33, 33. Since the high strength and high electrical resistance composite layer 32 has high strength and high electrical resistance, the rare eat magnet having high strength and high electrical resistance can be formed by providing the high strength and high electrical resistance composite layer 32 between the R—Fe—B-based rare earth magnet layers 31.

The glass layer of the high strength and high electrical resistance composite layer that constitutes the rare earth magnet having high strength and high electrical resistance may be any glass that is used in low temperature sintering of ceramics, such as SiO₂—B₂O₃—Al₂O₃-based glass, SiO₂—BaO—Al₂O₃-based glass, SiO₂—BaO—B₂O₃-based glass, SiO₂—BaO—Li₂O₃-based glass, SiO₂—B₂O₃—R-based glass (RrO represents an oxide of an alkaline earth metal), SiO₂—ZnO—RrO-based glass, SiO₂—MgO—Al₂O₃-based glass, SiO₂—B₂O₃—ZnO-based glass, B₂O₃—ZnO-based glass or SiO₂—Al₂O₃—RrO-based glass. In addition, glass having low softening point may also be used such as PbO—B₂O₃-based glass, SiO₂—B₂O₃—PbO-based glass, Al₂O₃—B₂O₃—PbO-based glass, Sn—P₂O₅-based glass, ZnO—P₂O₅-based glass, CuO-P₂O₅-based glass or SiO₂—B₂O₃—ZnO-based glass. It is preferable to use a glass that has softening point in a temperature range in which the hot pressing is carried out: from 500 to 900° C.

Another aspect of the present invention will be described.

FIG. 4 is a schematic sectional view of the rare earth magnet having high strength and high electrical resistance described in (8). In FIG. 4, components other than R—Fe—B-based rare earth magnet particles 18 are the same as those of the rare earth magnet 1 shown in FIG. 1, and will be omitted in the description that follows.

The rare earth magnet 4 having high strength and high electrical resistance of the present invention shown in FIG. 4 has a structure such that the high strength and high electrical resistance composite layer 12 is provided in the grain boundaries between the R—Fe—B-based rare earth magnet particle 18 and the R—Fe—B-based rare earth magnet particle 18, so that the R—Fe—B-based rare earth magnet particles 18 are enclosed with the high strength and high electrical resistance composite layer 12. Thus high strength and high electrical resistance are achieved by the presence of the high strength and high electrical resistance composite layer 12 in the grain boundary between the R—Fe—B-based rare earth magnet particle 18 and the R—Fe—B-based rare earth magnet particle 18.

The glass-based layer 16 of the high strength and high electrical resistance composite layer 12 further improves the insulation property, and also makes the bonding with the R oxide particle-based mixture layer 17 stronger. In addition, the R oxide particle-based mixture layer 17 prevents the R—Fe—B-based rare earth magnet particles 18 and the glass-based layer 16 from reacting with each other, so that the magnetic property is prevented from decreasing and bonding strength is increased, thereby providing the rare earth magnet having high strength and high electrical resistance that is excellent also in magnetic property. Presence of the high strength and high electrical resistance composite layer 12 enables the rare earth magnet having high strength and high electrical resistance of the present invention to greatly improve the electrical resistance inside of the magnet so as to reduce the eddy current generated therein and thereby suppress the heat generation from the magnet significantly.

The high strength and high electrical resistance composite layer 12 may also include an R oxide layer formed on the surface of the R oxide particle-based mixture layer 17 opposite to the surface thereof that makes contact with the glass-based layer 16.

FIG. 5 is a schematic sectional view showing the rare earth magnet having high strength and high electrical resistance in the constitution that the rare earth magnet having high strength and high electrical resistance described in (8) has the R oxide layer, namely the rare earth magnet having high strength and high electrical resistance described in (9).

In FIG. 5, the constitution is the same as that of the rare earth magnet 4 shown in FIG. 4 except that the high strength and high electrical resistance composite layer 12 further contains an R oxide layer 19, and will be omitted in the description that follows.

The glass-based layer 16 and the R oxide layer 19 of the high strength and high electrical resistance composite layer 12 further improve the insulation property, and also make bonding with the R oxide particle-based mixture layer 17 stronger. In addition, the R oxide particle-based mixture layer 17 and the R oxide layer 19 prevent the R—Fe—B-based rare earth magnet particles 18 and the glass-based layer 16 from reacting with each other, so that the magnetic property is prevented from decreasing and bonding strength is increased. Presence of the high strength and high electrical resistance composite layer 12 increases the strength of the magnet as a whole and enables the magnet to endure severe vibration, greatly improve the electrical resistance inside of the magnet so as to reduce the eddy current generated therein and thereby suppress the heat generation from the magnet significantly, and make the rare earth magnet excellent also in the magnet property.

FIG. 6 is a schematic sectional view showing the rare earth magnet having high strength and high electrical resistance described in (21). In FIG. 6, the constitution is the same as that of the rare earth magnet 3 shown in FIG. 3 except that R—Fe—B-based rare earth magnet particles 35 are contained, and will be omitted in the description that follows.

The rare earth magnet having high strength and high electrical resistance of the present invention shown in FIG. 6 has a structure such as the high strength and high electrical resistance composite layer 32 constituted from the R oxide layers 33, 33 and the glass layer 34 in the grain boundary between the R—Fe—B-based rare earth magnet particles 35, and the R—Fe—B-based rare earth magnet particles 35 are enclosed with the high strength and high electrical resistance composite layer 32. Presence of the high strength and high electrical resistance composite layer 32 in the grain boundary between the R—Fe—B-based rare earth magnet particles 35 and the R—Fe—B-based rare earth magnet particles 35 results in stronger bonding between the R oxide layers 33 due to the glass layer 34 of the high strength and high electrical resistance composite layer 32, so that the mechanical strength of the rare earth magnet is greatly improved and insulation property is also improved, thus achieving high strength and high electrical resistance.

Presence of the high strength and high electrical resistance composite layer 32 enables the rare earth magnet having high strength and high electrical resistance of the present invention to greatly improve the electrical resistance inside of the magnet so as to reduce the eddy current generated therein and thereby suppress the heat generation from the magnet significantly.

The R—Fe—B-based tare earth magnet particles 18 and 35 may be a rare earth magnet powder of a composition such that 5 to 20% of R and 3 to 20% of B are contained with the balance consisting of Fe and inevitable impurities, or a rare earth magnet powder of a composition such that 5 to 20% of R, 3 to 20% of B, and 0.001 to 5% of M are contained with the balance consisting of Fe and inevitable impurities, or a rare earth magnet powder of a composition such that 5 to 20% of R, 0.1 to 50% of Co, and 3 to 20% of B are contained with the balance consisting of Fe and inevitable impurities, or a rare earth magnet powder of a composition such that 5 to 20% of R, 0.1 to 50% of Co, 3 to 20% of B, and 0.001 to 5% of M are contained with the balance consisting of Fe and inevitable impurities.

In the rare earth magnet having high strength and high electrical resistance represented by FIG. 4, the glass-based layer 16 is preferably formed by softening and fusing the glass powder to form a glass phase or causing the R oxide particles to disperse in the softened glass phase during the hot pressing process, and the R oxide particle-based mixture layer 17 is preferably formed by causing the R-rich alloy phase which contains 50 atomic % or more of R contained in the R—Fe—B-based rare earth magnet particles 18 to enter the grain boundary of the R oxide particles during the hot pressing process.

R of the R oxide particles 13 that constitute the high strength and high electrical resistance composite layer 12 may or may not be the same as the R contained in the R—Fe—B-based rare earth magnet particles 18, it is preferably one or more selected from the group consisting of Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and is more preferably Tb and/or Dy.

R of the R-rich alloy layer 14 is preferably the same as the R of the R—Fe—B-based rare earth magnet particles 18, but may also be different from the R of the R—Fe—B-based rare earth magnet particles 18.

In the rare earth magnet having high strength and high electrical resistance represented by FIG. 5, the high strength and high electrical resistance composite layer 12 is formed in a structure such that the R oxide particle-based mixture layers 17 are formed on both sides of the glass-based layer 16 in contact therewith and has the R oxide layer 19 formed on the surface of the R oxide particle-based mixture layer 17 opposite to the surface thereof that makes contact with the glass-based layer 16. The high strength and high electrical resistance composite layer 12 encloses the R—Fe—B-based rare earth magnet particles 18.

It is preferable that the glass-based layer 16 is formed by softening and fusing the glass powder to form the glass phase or causing the R oxide particles to disperse in the softened glass phase during formation by hot pressing, and the R oxide particle-based mixture layer 17 is formed by causing the R-rich alloy phase which contains 50 atomic % or more of R contained in the R—Fe—B-based rare earth magnet particles 18 to enter the grain boundary of the R oxide particles during formation by hot pressing.

Thus, the R oxide particle-based mixture layer 7 is formed as the R-rich alloy phase which contains 50 atomic % or more of R contained in the R—Fe—B-based rare earth magnet particles 18 enters through a portion of the R oxide layer 19 where it is cracked or peeled off into the grain boundary of the R oxide particles during formation by hot pressing.

While R of the R oxide layer 13 and R of the R oxide layer 19 that constitute the high strength and high electrical resistance composite layer 12 may or may not be the same as the R contained in the R—Fe—B-based rare earth magnet particles 18, it is preferably one or more selected from the group consisting of Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and is more preferably Tb and/or Dy. Also R of the R-rich alloy layer 14 is preferably the same as the R of the R—Fe—B-based rare earth magnet particles 18, but may also be different from the R of the R—Fe—B-based rare earth magnet particles 18.

In the rare earth magnet having high strength and high electrical resistance represented by FIG. 6, while k of the R oxide layer 33 that constitutes the high strength and high electrical resistance composite layer 32 may or may not be the same as the R contained in the R—Fe—B-based rare earth magnet layer 31, it is preferably one or more kinds from the group consisting of Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and is more preferably Tb and/or Dy.

The R—Fe—B-based rare earth magnet particles 18 and 35 are preferably magnetically anisotropic HDDR magnetic particles having a fundamental structure shaving a recrystallization texture consisting of adjoining recrystallized grains that are constituted from an R₂Fe₁₄B type intermetallic compound phase of substantially tetragonal structure as the main phase, while the recrystallization texture has a constitution such that 50% by volume or more of the recrystallized grains are those which have such a shape as the ratio b/a of the least grain size a and the largest grain size b of the recrystallized grain is less tan 2, and average size of the recrystallized grains is in a range from 0.05 to 5 μm.

An example of manufacturing the R—Fe—B-based rare earth magnet particles of the rare earth magnet having high strength and high electrical resistance of the present invention is as follows.

An alloy material, that has a composition such that 5 to 20% of R and 3 to 20% of B are contained, or 0.1 to 50% of Co is also additionally contained as required, or 0.001 to 5% of M is further additionally contained as required, with the balance consisting of Fe and inevitable impurities, is crushed so as to achieve the average particle size in a range from 10 to 1000 μm by hydrogen absorption decay crushing or by the common crushing process in an inert gas atmosphere, so as to prepare the R—Fe—B-based rare earth magnet alloy material powder. The R—Fe—B-based rare earth magnet alloy material powder, with hydrogenated rare earth element powder mixed therein as required, is heated to a temperature below 500° C. in hydrogen gas atmosphere of pressure in a range from 10 to 1000 kPa, or heated and kept at this temperature, thereby to apply hydrogen absorption treatment. Then, the R—Fe—B-based rare earth magnet alloy material is heated to a temperature in a range from 500 to 1000° C. in hydrogen gas atmosphere of pressure in a range from 10 to 1000 kPa, and kept at this temperature, thereby to apply hydrogen absorption and decomposition treatment to the mixed powder. Then, as required, the mixed powder that has been subjected to the hydrogen absorption and decomposition treatment is subjected to intermediate heat treatment by keeping it at a temperature in a range from 500 to 1000° C. in an inert gas atmosphere of pressure in a range from 10 to 1000 kPa. Then, as required, the mixed powder that has been subjected to the intermediate heat treatment is subjected to heat treatment in reduced pressure hydrogen while letting a part of hydrogen remain in the mixed powder at a temperature in a range from 500 to 1000° C. in hydrogen atmosphere of pressure in a range from 0.65 to 10 kPa, or in a mixed gas atmosphere of hydrogen with partial pressure of 0.65 to 10 kPa and an inert gas. This is followed by dehydrogenation treatment in which the powder is kept in vacuum of 0.13 kPa or lower pressure at a temperature in a range from 500 to 1000° C. so as to force the powder to release hydrogen. The material is then cooled and crushed so as to make R—Fe—B-based HDDR rare earth magnet alloy powder. It is preferable that the R—Fe—B-based rare earth magnet particles are made by using the R—Fe—B-based HDDR rare earth magnet alloy powder.

An example of manufacturing the rare earth magnet having high strength and high electrical resistance of the present invention is as follows.

The R oxide particles are adhered by using PVA (polyvinyl alcohol) onto the surface of the ordinary HDDR rare earth magnet powder of high magnetic anisotropy, and glass powder is firth& adhered thereon with PVA, thereby to prepare a coated rare earth magnet powder. The coated rare earth magnet powder is subjected to heat treatment at a temperature in a range from 400 to 500° C. in vacuum so as to remove the PVA, followed by forming in a magnetic field and hot pressing, thereby making the rare earth magnet.

The hot-pressed material thus obtained has a structure such that the particles of the rare earth element powder 18 are enclosed with the high strength and high electrical resistance composite layer 12 as shown in FIG. 4 and FIG. 5, so that the rare earth magnet having high strength and high electrical resistance is formed due to high strength and high electrical resistance of the high strength and high electrical resistance composite layer 12.

When manufacturing the rare earth magnet having high strength and high electrical resistance represented by FIG. 5, instead of the process of adhering the R oxide particles on the surface of the HDDR rare earth element powder by means of PVA, oxide of R is formed on the surface of the R—Fe—B-based rare earth magnet powder so as to make oxide-coated R—Fe—B-based rare earth magnet powder by means of a sputtering apparatus that employs a rotary barrel, for example, and R oxide particles are adhered onto the surface of the oxide-coated R—Fe—B-based rare earth magnet powder by means of PVA.

An example of manufacturing the rare earth magnet having high strength and high electrical resistance represented by FIG. 6 is as follows.

The R oxide layer is adhered by means of a sputtering apparatus that employs a rotary barrel, for example, onto the surface of the ordinary R—Fe—B-based rare earth magnet powder of high magnetic anisotropy, thereby to prepare oxide-coated R—Fe—B-based rare earth magnet powder. A mixture of the oxide-coated R—Fe—B-based rare earth magnet powder and glass powder is formed in a magnetic field and hot pressing process is carried out, thereby making the rare earth magnet.

As shown in FIG. 6, the hot-pressed material thus obtained has a structure such that the particles of the R—Fe—B-based rare earth element powder 35 are enclosed with the high strength and high electrical resistance composite layer 32, so that the rare earth magnet having high strength and high electrical resistance is formed due to high strength and high electrical resistance of the high strength and high electrical resistance composite layer 32.

The glass layer of the high strength and high electrical resistance composite layer that constitutes the rare earth magnet having high strength and high electrical resistance may be any glass that is used in low temperature sintering of ceramics, such as SiO₂—B₂O₃—Al₂O₃-based glass, SiO₂—BaO—Al₂O₃-based glass, SiO₂—BaO—B₂O₃-based glass, SiO₂—BaO—Li₂O₃-based glass, SiO₂—B₂O₃—RrO based glass (RrO represents an oxide of an alkaline earth metal), SiO₂—ZnO—RrO-based glass, SiO₂—MgO—Al₂O₃-based glass, SiO₂—B₂O₃—ZnO-based glass, B₂O₃—ZnO-based glass, or SiO₂—Al₂O₃—RrO-based glass. In addition, glass having low softening point may also be used such as PbO—B₂O₃-based glass, SiO₂—B₂O₃—PbO-based glass, Al₂O₃—B₂O₃—PbO-based glass, SnO—P₂O₅-based glass, ZnO—P₂O₅-based glass, CuO—P₂O₅-based glass, or SiO₂O—B₂O₃—ZnO-based glass. It is preferable to use a glass that has softening point in a temperature range in which the hot pressing is carried out: from 500 to 900° C.

EXAMPLES

R—Fe—B-based rare earth magnet powders A through T, that had been subjected to HDDR treatment and had the compositions shown in Table 1, all having the average particle size of 300 μm were prepared.

TABLE 1 Types Composition (atomic %) (with the balance consisting of Fe) R—Fe—B- A Nd: 13%, Dy: 1.5%, Co: 5.8%, B: 6.2%, Zr: 0.1%, based rare Ga: 0.4% earth B Nd: 12.4%, Dy: 0.6%, Co: 20%, B: 6.2%, Zr: 0.1%, magnet Ga: 0.4%, Al: 1.5% powders C Nd: 13.5%, Co: 17.0%, B: 6.5%, Zr: 0.1%, Ga: 0.3% D Nd: 11.6%, Dy: 1.8%, Pr: 0.2%, B: 6.1% E Nd: 12.5%, Dy: 0.8%, Pr: 0.2%, Co: 7.0%, B: 6.5%, Zr: 0.1%, Ti: 0.3% F Nd: 12.5%, Pr: 0.5%, Co: 18.0%, B: 6.5%, Zr: 0.1%, Ga: 0.3% G Nd: 12.9%, Ho: 0.4%, Co: 14.7%, B: 6.8%, Hf: 0.1%, Si: 0.1%, W: 0.5% H Nd: 12.0%, Dy: 1.8%, B: 6.5%, Hf: 0.1% I Nd: 12.3%, Dy: 1.8%, Co: 16.9%, B: 6.6%, Zr: 0.2%, Ga: 0.3%, Al: 0.5% J Nd: 11.0%, Pr: 3.0%, Co: 20.0%, B: 6.5%, Ga: 0.3%, Si: 0.1% K Nd: 9.0%, Lu: 4.0%, Co: 10.0%, B: 6.5%, Nb: 0.4% L Nd: 8.0%, Dy: 5.0%, Co: 5.0%, B: 6.5%, Zr: 0.1%, Ta: 0.4% M Nd: 11.4%, Dy: 2.1%, Co: 15.0%, B: 7.0% N Nd: 12.2%, Tb: 1.2%, Co: 12.0%, B: 7.5%, Ge: 0.3%, Cr: 0.1% O Nd: 11.3%, Pr: 2.0%, Gd: 0.1%, B: 6.8%, V: 0.1%, Cu: 0.1% P Nd: 12.4%, Dy: 1.0%, Co: 8.0%, B: 6.5%,Ni: 0.1%, Mo: 0.3% Q Nd: 11.2%, Pr: 1.6%, Co: 11.2%, B: 6.5%, Zr: 0.1%, Ga: 0.3%, C: 0.2% R Nd: 13.0%, Dy: 1.0%, Y: 0.5%, Co: 2.5%, B: 6.0%, Zr: 0.1%, Ga: 0.4% S Nd: 12.5%, Er: 1.0%, Co: 12.0%, B: 7.5%, Zr: 0.05%, Ga: 0.3% T Nd: 12.5%, Ho: 1.0%, B: 6.8%, Zr: 0.2%, Ga: 0.2%, Al: 1.5%

Example 1 Rare Earth Magnet Having High Strength and High Electrical Resistance Represented by FIG. 1

R—Fe—B-based rare earth magnet green compact layers having thickness of 3 mm were formed in a magnetic field from the R—Fe—B-based rare earth magnet powders A through T shown in Table 1.

R oxide powder slurries were formed from Dy₂O₃, Pr₂O₃, La₂O₃, Nd₂O₃, CeO₂, Tb₂O₃, Gd₂O₃, Pr₂O₃, Y₂O₃, Er₂O₃, and Sm₂O₃, and glass powders having compositions shown in Tables 2 through 5 with the average particle size of 2 μm were prepared. Top surface of the R—Fe—B-based rare earth magnet green compact layer is coated with the R oxide powder slurry so as to form R oxide powder slurry layer, which was further coated with a glass powder slurry so as to form a glass powder slurry layer, thereby making one of the stacked bodies. Furthermore, the R oxide powder slurry was applied to the top surface of another R—Fe—B-based rare earth magnet green compact layer so as to form an R oxide powder slurry layer, thereby making the other stacked body.

The stacked bodies were put together so as to provide the glass powder slurry layer, thereby making the stacked green compact. The stacked green compact was hot-pressed at a temperature of 750° C. under a pressure of 147 MPa, thereby making the rare earth magnets 1 through 20 of the present invention in the form of bulk measuring 10 mm in length, 10 mm in width and 6.5 mm in height. The rare earth magnets 1 through 20 of the present invention made in this way all showed the constitution shown in FIG. 1 in which the high strength and high electrical resistance composite layer 12 has a structure consisting of the glass-based layer 16 of the structure consisting of a glass phase or the R oxide particles dispersed in the glass phase, and the R oxide particle-based mixture layers 17 that have a mixed structure containing an R-rich alloy phase which contains 50 atomic % or more of R and the R oxide particles are formed on both sides of the glass-based layer 16, while the high strength and high electrical resistance composite layer 12 is provided between the R—Fe—B-based rare earth magnet layers 11, 11.

The rare earth magnets 1 through 20 of the present invention made as described above were polished on the top and bottom surfaces and four side faces thereof. A pair of voltage terminals were applied with a space of 4 mm from each other to the rare earth magnets 1 through 20 of the present invention that were polished, across one R—Fe—B-based rare earth magnet layer to the other R—Fe—B-based rare earth magnet layer of the side face including the high strength and high electrical resistance composite layer straddling the high strength and high electrical resistance composite layer. A pair of current terminals were applied with a space of 6 mm from each other so as to cross over the pair of voltage terminals. Resistance R=E/I (Ω) was calculated from the voltage drop E (V) across the voltage terminals when a predetermined current I (A) was flown between the current terminals, and resistance was calculated from cross sectional area A (approximately 100 mm²) and the distance d between the terminals (=4 mm) by formula R×A/d, with the results shown in Tables 2 through 5.

Remanence (Br (T)), coercivity (iHc (MA/m)), and maximum energy product (MHmax (kJ/m³)) of the rare earth magnets 1 through 20 of the present invention were measured, with the results shown in Tables 2 through 5, and then, transverse rupture strength of the rare earth magnets 1 through 20 of the present invention were measured, with the results shown in Tables 2 through 5.

Comparative Example 1

Two of the other stacked bodies having the R oxide powder slurry layer formed thereon by applying the R oxide powder slurry on the top surface of the R—Fe—B-based rare earth magnet green compact layer made in Example 1 were prepared. The stacked bodies were put together with the R oxide particle slurry layers facing each other so as to form the stacked green compact constituted from the R—Fe—B-based rare earth magnet green compact layer, the R oxide powder slurry layer, the R oxide powder slurry layer and the R—Fe—B-based rare earth magnet green compact layer. The stacked green compact was hot-pressed at a temperature of 750° C. under a pressure of 147 MPa, thereby making the rare earth magnets 1 through 20 of the prior art in the form of bulk constituted from the R—Fe—B-based rare earth magnet layer and the R oxide layer measuring 10 mm in length, 10 mm in width and 6.5 mm in thickness.

The rare earth magnets 1 through 20 of the present invention made as described above were polished on the top and bottom surfaces and four side faces thereof. A pair of voltage terminals were applied with a space of 4 mm from each other to the rare earth magnets 1 through 20 of the present invention that were polished, across one R—Fe—B-based rare earth magnet layer to the other R—Fe—B-based rare earth magnet layer of the side face including the oxide layer while straddling the R oxide layer. A pair of current terminals were applied with a space of 6 mm from each other so as to cross over the pair of voltage terminals. Resistance R=E/I (Ω) was calculated from the voltage drop E (V) across the voltage terminals when a predetermined current I (A) was flown between the current terminals, and resistance was calculated from cross sectional area A (approximately 100 mm²) and the distance d between the terminals (=4 mm) by formula R×A/d, with the results shown in Tables 2 through 5.

Remanence, coercivity and maximum energy product of the rare earth magnets 1 through 20 of the prior art were measured, with the results shown in Tables 2 through 5, then transverse rupture strength of the rare earth magnets 1 through 20 of the prior art were measured, with the results shown in Tables 2 through 5.

TABLE 2 High strength and high electrical resistance composite layer R oxide particle- Properties Composition of based mixture Transverse R—Fe—B-based layer Glass-based layer Resis- rupture Rare earth rare earth magnet R oxide Alloy R oxide Content of glass Br iHc BHmax tivity strength magnet layer particles phase particles layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 1 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—RrO 1.19 1.81 251 480 119 invention rare earth magnet phase Prior art powder A Dy₂O₃ 1.19 1.79 251 21 23 Present 2 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—ZnO 1.23 1.50 267 620 129 invention rare earth magnet phase Prior art powder B Dy₂O₃ 1.23 1.49 268 24 24 Present 3 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—RrO 1.24 1.02 273 1190 163 invention rare earth magnet phase Prior art powder C Dy₂O₃ 1.24 1.01 273 28 25 Present 4 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—Al₂O₃ 1.16 1.50 239 3430 230 invention rare earth magnet phase Prior art powder D Dy₂O₃ 1.16 1.48 241 45 26 Present 5 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—BaO—Al₂O₃ 1.19 1.54 251 1610 117 invention rare earth magnet phase Prior art powder E Dy₂O₃ 1.19 1.52 251 38 24

TABLE 3 High strength and high electrical resistance composite layer R oxide particle- Properties Composition of based mixture Transverse R—Fe—B-based layer Glass-based layer Resis- rupture Rare earth rare earth magnet R oxide Alloy R oxide Content of Br iHc BHmax tivity strength magnet layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 6 R—Fe—B-based Pr₂O₃ R-rich Pr₂O₃ SiO₂—BaO—B₂O₃ 1.21 1.17 262 2290 200 invention rare earth magnet phase Prior art powder F Pr₂O₃ 1.21 1.15 262 33 27 Present 7 R—Fe—B-based Ho₂O₃ R-rich Ho₂O₃ SiO₂—BaO—Li₂O₃ 1.18 1.13 246 460 119 invention rare earth magnet phase Prior art powder G Ho₂O₃ 1.18 1.12 246 23 23 Present 8 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—MgO—Al₂O₃ 1.15 1.71 234 3500 231 invention rare earth magnet phase Prior art powder H Dy₂O₃ 1.15 1.69 236 35 28 Present 9 R—Fe—B-based Nd₂O₃ R-rich Nd₂O₃ SiO₂—ZnO—BrO 1.17 1.63 245 2800 215 invention rare earth magnet phase Prior art powder I Nd₂O₃ 1.17 1.61 245 50 24 Present 10 R—Fe—B-based Nd₂O₃ R-rich Nd₂O₃ SiO₂—B₂O₃—ZnO 1.19 1.16 251 1870 180 invention rare earth magnet phase Prior art powder J Nd₂O₃ 1.19 1.15 251 40 24

TABLE 4 High strength and high electrical resistance composite layer R oxide particle- Properties Composition of based mixture Transverse R—Fe—B-based layer Glass-based layer Resis- rupture Rare earth rare earth magnet R oxide Alloy R oxide Content of Br iHc BHmax tivity strength magnet layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 11 R—Fe—B-based Lu₂O₃ R-rich Lu₂O₃ SiO₂—Al₂O₃—RrO 1.18 0.98 246 1310 166 invention rare earth magnet phase Prior art powder K Lu₂O₃ 1.18 0.97 246 25 26 Present 12 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ B₂O₃—ZnO 1.21 1.84 262 1940 190 invention rare earth magnet phase Prior art powder L Dy₂O₃ 1.21 1.83 262 43 24 Present 13 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ PbO—B₂O₃ 1.17 1.59 245 3240 224 invention rare earth magnet phase Prior art powder M Dy₂O₃ 1.17 1.58 245 58 23 Present 14 R—Fe—B-based Tb₂O₃ R-rich Tb₂O₃ SiO₂—B₂O₃—PbO 1.16 1.48 239 2480 207 invention rare earth magnet phase Prior art powder N Tb₂O₃ 1.16 1.47 241 48 24 Present 15 R—Fe—B-based Gd₂O₃ R-rich Gd₂O₃ Al₂O₃—B₂O₃—PbO 1.20 1.14 256 1260 161 invention rare earth magnet phase Prior art powder O Gd₂O₃ 1.20 1.13 257 35 24

TABLE 5 High strength and high electrical resistance composite layer R oxide particle- Properties Composition of based mixture Transverse R—Fe—B-based layer Glass-based layer rupture Rare earth rare earth magnet R oxide Alloy R oxide Content of Br iHc BHmax Resistivity strength magnet layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 16 R—Fe—B-based Dy₂O₃ R-rich — SnO—P₂O₅ 1.19 1.54 251 1010 154 invention rare earth magnet phase Prior art powder P Dy₂O₃ 1.19 1.52 252 25 23 Present 17 R—Fe—B-based Pr₂O₃ R-rich — ZnO—P₂O₅ 1.21 1.06 261 1820 181 invention rare earth magnet phase Prior art powder Q Pr₂O₃ 1.21 1.05 262 38 25 Present 18 R—Fe—B-based Y₂O₃ R-rich — ZnO—P₂O₅ 1.13 1.66 229 1950 188 invention rare earth magnet phase Prior art powder R Y₂O₃ 1.14 1.65 231 35 26 Present 19 R—Fe—B-based Er₂O₃ R-rich — CuO—P₂O₅ 1.16 1.51 240 1520 176 invention rare earth magnet phase Prior art powder S Er₂O₃ 1.16 1.50 241 30 26 Present 20 R—Fe—B-based Ho₂O₃ R-rich — SiO₂—B₂O₃—ZnO 1.19 1.40 250 1870 182 invention rare earth magnet phase Prior art powder T Ho₂O₃ 1.19 1.39 251 38 25

From the results shown in Tables 2 through 5, it can be seen that the rare earth magnets 1 through 20 of the present invention have particularly higher strength and higher electrical resistance than the rare earth magnets 1 through 20 of the prior art.

Example 2

R oxide powders made of Dy₂O₃, Pr₂O₃, La₂O₃, Nd₂O₃, CeO₂, Tb₂O₃, Gd₂O₃, Pr₂O₃, Y₂O₃, Er₂O₃, and Sm₂O₃ were adhered using 0.1% by weight of PVA to the surface of the R—Fe—B-based rare earth magnet powders A through T previously prepared by HDDR treatment shown in Table 1, to a thickness of 2 μm, and glass powders shown in Tables 6 through 9 were further adhered thereon with 0.1% by weight of PVA (polyvinyl alcohol), thereby to prepare the oxide-coated R—Fe—B-based rare earth magnet powder. The oxide-coated R—Fe—B-based rare earth magnet powder was subjected to heat treatment at a temperature of 450° C. in vacuum so as to remove the PVA, followed by preliminary forming in a magnetic field under a pressure of 49 MPa and hot pressing at a temperature of 730° C. under a pressure of 294 MPa, thereby making the rare earth magnets 21 through 40 of the present invention in the form of bulk measuring 10 mm in length, 10 mm in width, and 7 mm in height. The rare earth magnets 21 through 40 of the present invention showed the constitution shown in FIG. 4 in which the high strength and high electrical resistance composite layer 12 comprising the glass-based layer 16, which had the structure consisting of a glass phase or R oxide particles dispersed in glass phase, and the R oxide particle-based mixture layers 17, that had mixed structure of the R-rich alloy phase which contained 50 atomic % or more of R and the R oxide particles, and were formed on both sides of the glass-based layer 16, enclosed the R—Fe—B-based rare earth magnet particles 18.

The rare earth magnets 21 through 40 of the present invention in the form of bulk made as described above were polished on the surfaces thereof, and resistivity was measured with the results shown in Tables 6 through 9.

Remanence, coercivity and maximum energy product of the rare earth magnets 21 through 40 of the present invention were measured by the ordinary methods, with the results shown in Tables 6 through 9, then transverse rupture strength of the rare earth magnets 21 through 40 of the present invention were measured, with the results shown in Tables 6 through 9.

Comparative Example 2

The oxide-coated R—Fe—B-based rare earth magnet powder made in Example 2 was subjected to preliminary forming in a magnetic field under a pressure of 49 MPa and then subjected to hot pressing at a temperature of 730° C. under a pressure of 294 MPa, thereby making the rare earth magnets 21 through 40 of the prior art in the form of bulk measuring 10 mm in length, 10 mm in width, and 7 mm in height having a structure such that the R—Fe—B-based rare earth magnet particles were enclosed with the R oxide layers.

The rare earth magnets 21 through 40 of the prior art in the form of bulk made as described above were polished on the surface, and resistivity was measured on each one with the results shown in Tables 6 through 9.

Remanence, coercivity and maximum energy product of the rare earth magnets 21 through 40 of the prior art were measured by the ordinary methods, with the results shown in Tables 6 through 9, then transverse rupture strength of the rare earth magnets 21 through 40 of the prior art were measured, with the results shown in Tables 6 through 9.

TABLE 6 High strength and high electrical resistance composite layer R oxide particle- Properties Composition of based mixture Transverse R—Fe—B-based layer Glass-based layer Resis- rupture Rare earth rare earth magnet R oxide Alloy R oxide Content of Br iHc BHmax tivity strength magnet layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 21 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—RrO 1.16 1.81 238 2180 193 invention rare earth magnet phase Prior art powder A Dy₂O₃ 1.18 1.79 246 47 38 Present 22 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—ZnO 1.17 1.50 246 3650 201 invention rare earth magnet phase Prior art powder B Dy₂O₃ 1.20 1.49 257 56 21 Present 23 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—RrO 1.17 1.02 245 620 117 invention rare earth magnet phase Prior art powder C Dy₂O₃ 1.21 1.01 259 32 25 Present 24 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—Al₂O₃ 1.06 1.50 202 2230 173 invention rare earth magnet phase Prior art powder D Dy₂O₃ 1.11 1.48 221 50 29 Present 25 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—BaO—Al₂O₃ 1.06 1.54 201 4630 230 invention rare earth magnet phase Prior art powder E Dy₂O₃ 1.12 1.52 224 66 36

TABLE 7 High strength and high electrical resistance composite layer R oxide particle- Properties Composition of based mixture Transverse R—Fe—B-based layer Glass-based layer Resis- rupture Rare earth rare earth magnet R oxide Alloy R oxide Content of Br iHc BHmax tivity strength magnet layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 26 R—Fe—B-based Pr₂O₃ R-rich Pr₂O₃ SiO₂—BaO—B₂O₃ 1.10 1.17 215 3590 210 invention rare earth magnet phase Prior art powder F Pr₂O₃ 1.15 1.15 235 63 27 Present 27 R—Fe—B-based Ho₂O₃ R-rich Ho₂O₃ SiO₂—BaO—Li₂O₃ 1.06 1.13 199 3630 210 invention rare earth magnet phase Prior art powder G Ho₂O₃ 1.10 1.12 217 72 28 Present 28 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ SiO₂—MgO—Al₂O₃ 0.90 1.71 145 1480 175 invention rare earth magnet phase Prior art powder H Dy₂O₃ 1.02 1.69 185 46 23 Present 29 R—Fe—B-based Nd₂O₃ R-rich Nd₂O₃ SiO₂—ZnO—BrO 1.05 1.63 197 1340 150 invention rare earth magnet phase Prior art powder I Nd₂O₃ 1.11 1.61 220 43 25 Present 30 R—Fe—B-based Nd₂O₃ R-rich Nd₂O₃ SiO₂—B₂O₃—ZnO 1.11 1.16 220 1190 149 invention rare earth magnet phase Prior art powder J) Nd₂O₃ 1.15 1.15 236 36 35

TABLE 8 High strength and high electrical resistance composite layer R oxide particle- Properties Composition of based mixture Transverse R—Fe—B-based layer Glass-based layer Resis- rupture Rare earth rare earth magnet R oxide Alloy R oxide Content of Br iHc BHmax tivity strength magnet layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 31 R—Fe—B-based Lu₂O₃ R-rich Lu₂O₃ SiO₂—Al₂O₃—RrO 1.13 0.98 228 770 144 invention rare earth magnet phase Prior art powder K Lu₂O₃ 1.16 0.97 238 33 26 Present 32 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ B₂O₃—ZnO 1.19 1.84 254 560 122 invention rare earth magnet phase Prior art powder L Dy₂O₃ 1.21 1.83 259 30 34 Present 33 R—Fe—B-based Dy₂O₃ R-rich Dy₂O₃ PbO—B₂O₃ 1.08 1.59 208 1650 179 invention rare earth magnet phase Prior art powder M Dy₂O₃ 1.13 1.58 226 48 22 Present 34 R—Fe—B-based Tb₂O₃ R-rich Tb₂O₃ SiO₂—B₂O₃—PbO 1.07 1.48 205 1570 159 invention rate earth magnet phase Prior art powder N Tb₂O₃ 1.12 1.47 223 45 20 Present 35 R—Fe—B-based Gd₂O₃ R-rich Gd₂O₃ Al₂O₃—B₂O₃—PbO 1.12 1.14 223 1090 143 invention rare earth magnet phase Prior art powder O Gd₂O₃ 1.16 1.13 239 41 29

TABLE 9 High strength and high electrical resistance composite layer R oxide particle- Properties Composition of based mixture Transverse R—Fe—B-based layer Glass-based layer rupture Rare earth rare earth magnet R oxide Alloy R oxide Content of Br iHc BHmax Resistivity strength magnet layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 36 R—Fe—B-based Dy₂O₃ R-rich — SnO—P₂O₅ 1.11 1.54 221 890 129 invention rare earth magnet phase Prior art powder P Dy₂O₃ 1.15 1.52 236 37 26 Present 37 R—Fe—B-based Pr₂O₃ R-rich — ZnO—P₂O₅ 1.13 1.06 226 1390 154 invention rare earth magnet phase Prior art powder Q Pr₂O₃ 1.17 1.05 245 40 33 Present 38 R—Fe—B-based Y₂O₃ R-rich — ZnO—P₂O₅ 1.05 1.66 195 1810 165 invention rare earth magnet phase Prior art powder R Y₂O₃ 1.10 1.65 214 44 26 Present 39 R—Fe—B-based Er₂O₃ R-rich — CuO—P₂O₅ 1.08 1.51 207 1220 162 invention rare earth magnet phase Prior art powder S Er₂O₃ 1.13 1.50 225 39 36 Present 40 R—Fe—B-based Ho₂O₃ R-rich — SiO₂—B₂O₃—ZnO 1.12 1.40 223 850 117 invention rare earth magnet phase Prior art powder T Ho₂O₃ 1.16 1.39 238 33 32

From the results shown in Tables 6 through 9, it can be seen that the rare earth magnets 21 through 40 of the present invention have particularly higher strength and higher electrical resistance than the rare earth magnets 21 through 40 of the prior art.

Example 3

R—Fe—B-based rare earth magnet green compact layers having thickness of 4 mm were formed in magnetic field from the R—Fe—B-based rare earth magnet powders A through T shown in Table 1.

R oxide targets made from Dy₂O₃, Pr₂O₃, La₂O₃, Nd₂O₃, CeO₂, Tb₂O₃, Gd₂O₃, Pr₂O₃, Y₂O₃, Er₂O₃, and Sm₂O₃ were prepared.

Sputtered layers of R oxide having thickness of 3 μm and compositions shown in Tables 10 through 13 were formed on the surface of the R—Fe—B-based rare earth magnet green compact layer by means of a sputtering apparatus.

R oxide powder slurries formed from Dy₂O₃, Pr₂O₃, La₂O₃, Nd₂O₃, CeO₂, Tb₂O₃, Gd₂O₃, Pr₂O₃, Y₂O₃, Er₂O₃, and Sm₂O₃, and glass powders having compositions shown in Tables 10 through 13 with the average particle size of 2 μm were prepared. The top surface of the sputtered layers of R oxide formed on the R—Fe—B-based rare earth magnet green compact layer was coated with the R oxide powder slurry so as to form the R oxide powder slurry layer. A glass powder slurry was further applied to the R oxide powder slurry layer so as to form a glass powder slurry layer on the R oxide powder slurry layer, thereby making one of the stacked bodies.

Furthermore, the R oxide powder slurry was applied to the top surface of another R—Fe—B-based rare earth magnet green compact layer whereon the sputtered layers of R oxide was formed so as to form R oxide powder slurry layer, thereby making the other stacked body.

The glass powder slurry layer is provided between the stacked bodies so as to prepare a stacked green compact. The stacked green compact was hot-pressed at a temperature of 750° C. under a pressure of 147 MPa, thereby making the rare earth magnets 41 through 60 of the present invention in the form of bulk measuring 10 mm in length, 10 mm in width, and 6.5 mm in height, The rare earth magnets 41 through 60 of the present invention made in this way all showed the constitution shown in FIG. 2 in which the high strength and high electrical resistance composite layer 12 had a structure such that the glass-based layer 16, which had the structure consisting of a glass phase or the R oxide particles dispersed in the glass phase, was provided between the R oxide particle-based mixture layers 17, that had a mixed structure of an R-rich alloy phase which contained 50 atomic % or more of R and the R oxide particles, in contact with the glass-based layer 16, and the R oxide layer 19 was stacked on the surface of the R oxide particle-based mixture layers 17 opposite to the surface thereof that made contact with the glass-based layer 16, while the high strength and high electrical resistance composite layer 12 was provided between the R—Fe—B-based rare earth magnet layers 11, 11.

The rare earth magnets 41 through 60 of the present invention made as described above were polished on the top and bottom surfaces and four side faces thereof. A pair of voltage terminals were applied with a space of 4 mm from each other to the rare earth magnets 41 through 60 of the present invention that were polished, across one R—Fe—B-based rare earth magnet layer to the other R—Fe—B-based rare earth magnet layer of the side face including the high strength and high electrical resistance composite layer while straddling the high strength and high electrical resistance composite layer. A pair of current terminals were applied with a space of 6 mm from each other so as to cross over the pair of voltage terminals. Resistance R=E/I (Ω) was calculated from the voltage drop E (V) across the voltage terminals when a predetermined current I (A) was flown between the current terminals, and resistance was calculated from cross sectional area A (approximately 100 mm²) and the distance d between the terminals (=4 mm) by formula R×A/d, with the results shown in Tables 2 through 5.

Remanence, coercivity and maximum energy product of the rare earth magnets 41 through 60 of the present invention were measured, with the results shown in Tables 10 through 13, then breaking resistance of the rare earth magnets 41 through 60 of the present invention was measured, with the results shown in Tables 13 through 13.

Comparative Example 3

Two stacked bodies having the R oxide powder slurry layers formed by applying the R oxide powder slurry on the top surface of the R—Fe—B-based rare earth magnet green compact layer made in Example 3 were prepared. The two stacked bodies were put together with the R oxide powder slurry layers facing each other so as to form the stacked green compact constituted from the R—Fe—B-based rare earth magnet green compact layer, the R oxide powder slurry layer, the R oxide powder slurry layer and the R—Fe—B-based rare earth magnet green compact layer. The stacked green compact was hot-pressed at a temperature of 750° C. under a pressure of 147 MPa, thereby making the rare earth magnets 41 through 60 of the prior art in the form of bulk constituted from the R—Fe—B-based rare earth magnet layer and the R oxide layer measuring 10 mm in length, 10 mm in width, and 6.5 mm in height.

The rare earth magnets 41 through 60 of the prior art made as described above were polished on the top and bottom surfaces and four side faces thereof. A pair of voltage terminals were applied with a space of 4 mm from each other to the rare earth magnets 41 through 60 of the prior art that were polished, across one R—Fe—B-based rare earth magnet layer to the other R—Fe—B-based rare earth magnet layer of the side face including the R oxide layer while straddling the R oxide layer. A pair of current terminals were applied with a space of 6 mm from each other so as to cross over the pair of voltage terminals. Resistance R=E/I (Ω) was calculated from the voltage drop E (V) across the voltage terminals when a predetermined current I (A) was flown between the current terminals, and resistance was calculated from the cross sectional area A (approximately 100 mm²) and the distance d between die terminals (=4 mm) by formula R×A/d, with the results shown in Tables 10 through 13.

Remanence, coercivity and maximum energy product of the rare earth magnets 41 through 60 of the prior art were measured by the ordinary methods, with the results shown in Tables 2 through 5, then transverse rupture strength of the rare earth magnets 41 through 60 of the prior art were measured, with the results shown in Tables 10 through 13.

TABLE 10 High strength and high electrical resistance composite layer Composition R oxide particle- Properties of R—Fe—B- based mixture Transverse based rare R layer Glass-based layer rupture Rare earth earth magnet oxide R oxide Alloy R oxide Content of Br iHc BHmax Resistivity strength magnet layer layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 41 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—RrO 1.19 1.81 251 570 128 invention rare earth phase magnet Prior art powder A Dy₂O₃ 1.19 1.79 251 21 23 Present 42 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—ZnO 1.23 1.50 267 1030 145 invention rare earth phase magnet Prior art powder B Dy₂O₃ 1.23 1.49 268 24 24 Present 43 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—RrO 1.24 1.02 272 1970 178 invention rare earth phase magnet Prior art powder C Dy₂O₃ 1.24 1.01 273 28 25 Present 44 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—Al₂O₃ 1.16 1.50 240 5140 255 invention rare earth phase magnet Prior art powder D Dy₂O₃ 1.16 1.48 241 45 26 Present 45 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—BaO—Al₂O₃ 1.19 1.54 250 2610 195 invention rare earth phase magnet Prior art powder E Dy₂O₃ 1.19 1.52 251 38 24

TABLE 11 High strength and high electrical resistance composite layer Composition R oxide particle- Properties of R—Fe—B- based mixture Transverse based rare R layer Glass-based layer rupture Rare earth earth magnet oxide R oxide Alloy R oxide Content of Br iHc BHmax Resistivity strength magnet layer layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 46 R—Fe—B-based Pr₂O₃ Pr₂O₃ R-rich Pr₂O₃ SiO₂—BaO—B₂O₃ 1.21 1.17 261 3810 223 invention rare earth phase magnet Prior art powder F Pr₂O₃ 1.21 1.15 262 33 27 Present 47 R—Fe—B-based Ho₂O₃ Ho₂O₃ R-rich Ho₂O₃ SiO₂—BaO—Li₂O₃ 1.18 1.13 246 650 131 invention rare earth phase magnet Prior art powder G Ho₂O₃ 1.18 1.12 246 23 23 Present 48 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—MgO—Al₂O₃ 1.15 1.71 234 5740 256 invention rare earth phase magnet Prior art powder H Dy₂O₃ 1.15 1.69 236 35 28 Present 49 R—Fe—B-based Nd₂O₃ Nd₂O₃ R-rich Nd₂O₃ SiO₂—ZnO—BrO 1.17 1.63 245 4550 236 invention rare earth phase magnet Prior art powder I Nd₂O₃ 1.17 1.61 245 50 24 Present 50 R—Fe—B-based Nd₂O₃ Nd₂O₃ R-rich Nd₂O₃ SiO₂—B₂O₃—ZnO 1.19 1.16 250 2690 205 invention rare earth phase magnet Prior art powder J Nd₂O₃ 1.19 1.15 251 40 24

TABLE 12 High strength and high electrical resistance composite layer Composition R oxide particle- Properties of R—Fe—B- based mixture Transverse based rare R layer Glass-based layer rupture Rare earth earth magnet oxide R oxide Alloy R oxide Content of Br iHc BHmax Resistivity strength magnet layer layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 51 R—Fe—B-based Lu₂O₃ Lu₂O₃ R-rich Lu₂O₃ SiO₂—Al₂O₃—RrO 1.18 0.98 245 2180 186 invention rare earth phase Prior art magnet Lu₂O₃ 1.18 0.97 246 25 26 powder K Present 52 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ B₂O₃—ZnO 1.21 1.84 260 3230 211 invention rare earth phase Prior art magnet Dy₂O₃ 1.21 1.83 262 43 24 powder L Present 53 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ PbO—B₂O₃ 1.17 1.59 244 4700 243 invention rare earth phase Prior art magnet Dy₂O₃ 1.17 1.58 244 58 23 powder M Present 54 R—Fe—B-based Tb₂O₃ Tb₂O₃ R-rich Tb₂O₃ SiO₂—B₂O₃—PbO 1.16 1.48 240 4020 231 invention rare earth phase Prior art magnet Tb₂O₃ 1.16 1.47 241 48 24 powder N Present 55 R—Fe—B-based Gd₂O₃ Gd₂O₃ R-rich Gd₂O₃ Al₂O₃—B₂O₃—PbO 1.20 1.14 256 1940 176 invention rare earth phase Prior art magnet Gd₂O₃ 1.20 1.13 257 35 24 powder O

TABLE 13 High strength and high electrical resistance composite layer Composition R oxide particle- Properties of R—Fe—B- based mixture Transverse based rare R layer Glass-based layer rupture Rare earth earth magnet oxide R oxide Alloy R oxide Content of iHc BHmax Resistivity strength magnet layer layer particles phase particles glass layer Br (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 56 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich — SnO—P₂O₅ 1.19 1.54 250 1500 172 invention rare earth phase Prior art magnet Dy₂O₃ 1.19 1.52 252 25 25 powder P Present 57 R—Fe—B-based Pr₂O₃ Pr₂O₃ R-rich — ZnO—P₂O₅ 1.21 1.06 261 2770 201 invention rare earth phase Prior art magnet Pr₂O₃ 1.21 1.05 262 38 25 powder Q Present 58 R—Fe—B-based Y₂O₃ Y₂O₃ R-rich — ZnO—P₂O₅ 1.13 1.66 230 3030 214 invention rare earth phase Prior art magnet Y₂O₃ 1.14 1.65 231 35 26 powder R Present 59 R—Fe—B-based Er₂O₃ Er₂O₃ R-rich — CuO—P₂O₅ 1.16 1.51 240 2620 193 invention rare earth phase Prior art magnet Er₂O₃ 1.16 1.50 241 30 26 powder S Present 60 R—Fe—B-based Ho₂O₃ Ho₂O₃ R-rich — SiO₂—B₂O₃—ZnO 1.19 1.40 251 2940 204 invention rare earth phase Prior art magnet Ho₂O₃ 1.19 1.39 251 38 25 powder T

From the results shown in Tables 10 through 13, it can be seen that the rare earth magnets 41 through 60 of the present invention have particularly higher strength and higher electrical resistance than rare earth magnets 41 through 60 of the prior art.

Example 4

Sputtered layers of R oxide having thickness of 2 μm and compositions shown in Tables 10 through 13 were formed on the surfaces of the R—Fe—B-based rare earth magnet powders A through T that had been subjected to HDDR treatment shown in Table 1 by means of a sputtering apparatus that employed a rotary barrel, by using the R oxide target prepared in Example 1. R oxide powders made of Dy₂O₃, Pr₂O₃, La₂O₃, Nd₂O₃, CeO₂, Tb₂O₃, Gd₂O₃, Pr₂O₃, Y₂O₃, Er₂O₃, and Sm₂O₃ was adhered onto the layer described above using 0.1% by weight of PVA to a thickness of 2 μm, and glass powders shown in Tables 14 through 17 were further adhered thereon with 0.1% by weight of PVA (polyvinyl alcohol), thereby to prepare oxide-coated R—Fe—B-based rare earth magnet powder. The oxide-coated R—Fe—B-based-rare earth magnet powder was subjected to heat treatment at a temperature of 450° C. in vacuum so as to remove the PVA, followed by forming in a magnetic field under a pressure of 49 MPa and hot pressing at a temperature of 730° C. under a pressure of 294 MPa, thereby making the rare earth magnets 61 through 80 of the present invention in the form of bulk measuring 10 mm in length, 10 mm in width, and 7 mm in height. The rare earth magnets 61 through 80 of the present invention had a structure, as shown in FIG. 5, in which the R—Fe—B-based rare earth magnet particles 18 were enclosed with the high strength and high electrical resistance composite layer 12 comprising the glass-based layer 16, which had the structure consisting of the R oxide particles dispersed in glass phase, the R oxide particle-based mixture layers 17 having a mixed structure of an R-rich alloy phase containing 50 atomic % or more of R and the R oxide particles formed on both sides of the glass-based layer 16, and the R oxide layer 19.

The rare earth magnets 61 through 80 of the present invention in the form of bulk made as described above were polished on the surfaces thereof, and resistivity was measured with the results shown in Tables 14 through 17.

Remanence, coercivity, and maximum energy product of the rare earth magnets 61 through 80 of the present invention were measured by the ordinary methods, with the results shown in Tables 14 through 17, then transverse rupture strength of the rare earth magnets 61 through 80 of the present invention were measured, with the results shown in Tables 14 through 17.

Comparative Example 4

Covered powders formed by sputtering of the R oxide layers shown in Tables 14 through 17 on the surface of the R—Fe—B-based rare earth magnet powders made in Example 4 were preliminary formed in a magnetic field under a pressure of 49 MPa, followed by hot pressing at a temperature of 730° C. under a pressure of 294 MPa, thereby making the rare earth magnets 61 through 80 of the prior art having a structure such that the R—Fe—B-based rare earth magnet particles were enclosed with the R oxide layers in the form of bulk measuring 10 mm in length, 10 mm in width, and 7 mm in height.

The rare earth magnets 61 through 80 of the prior art in the form of bulk made as described above were polished on the surfaces thereof, and resistivity was measured with the results shown in Tables 14 through 17.

Remanence, coercivity, and maximum energy product of the rare earth magnets 61 through 80 of the prior art were measured by the ordinary methods, with the results shown in Tables 14 Trough 17, then transverse rupture strength of the rare earth magnets 61 through 80 of the prior art were measured, with the results shown in Tables 14 through 17.

TABLE 14 High strength and high electrical resistance composite layer Composition R oxide particle- Properties of R—Fe—B- based mixture Transverse based rare R layer Glass-based layer rupture Rare earth earth magnet oxide R oxide Alloy R oxide Content of Br iHc BHmax Resistivity strength magnet layer layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 61 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—RrO 1.16 1.81 238 4070 223 invention rare earth phase Prior art magnet Dy₂O₃ 1.18 1.79 246 47 38 powder A Present 62 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—ZnO 1.17 1.50 245 5700 238 invention rare earth phase Prior art magnet Dy₂O₃ 1.20 1.49 257 56 21 powder B Present 63 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—RrO 1.17 1.02 244 550 142 invention rare earth phase Prior art magnet Dy₂O₃ 1.21 1.01 259 32 25 powder C Present 64 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—B₂O₃—Al₂O₃ 1.06 1.50 201 3250 202 invention rare earth phase Prior art magnet Dy₂O₃ 1.11 1.48 221 50 29 powder D Present 65 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—BaO—Al₂O₃ 1.06 1.54 200 7980 263 invention rare earth phase Prior art magnet Dy₂O₃ 1.12 1.52 224 66 36 powder E

TABLE 15 High strength and high electrical resistance composite layer Composition R oxide particle- Properties of R—Fe—B- based mixture Transverse based rare R layer Glass-based layer rupture Rare earth earth magnet oxide R oxide Alloy R oxide Content of Br iHc BHmax Resistivity strength magnet layer layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 66 R—Fe—B-based Pr₂O₃ Pr₂O₃ R-rich Pr₂O₃ SiO₂—BaO—B₂O₃ 1.10 1.17 214 4910 223 invention rare earth phase Prior art magnet Pr₂O₃ 1.15 1.15 235 63 27 powder F Present 67 R—Fe—B-based Ho₂O₃ Ho₂O₃ R-rich Ho₂O₃ SiO₂—BaO—Li₂O₃ 1.06 1.13 198 6430 249 invention rare earth phase Prior art magnet Ho₂O₃ 1.10 1.12 217 72 28 powder G Present 68 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ SiO₂—MgO—Al₂O₃ 0.90 1.71 143 2800 189 invention rare earth phase Prior art magnet Dy₂O₃ 1.02 1.69 185 46 23 powder H Present 69 R—Fe—B-based Nd₂O₃ Nd₂O₃ R-rich Nd₂O₃ SiO₂—ZnO—BrO 1.05 1.63 196 1830 179 invention rare earth phase Prior art magnet Nd₂O₃ 1.11 1.61 220 43 25 powder I Present 70 R—Fe—B-based Nd₂O₃ Nd₂O₃ R-rich Nd₂O₃ SiO₂—B₂O₃—ZnO 1.11 1.16 219 1170 167 invention rare earth phase Prior art magnet Nd₂O₃ 1.15 1.15 236 36 35 powder J

TABLE 16 High strength and high electrical resistance composite layer Composition R oxide particle- Properties of R—Fe—B- based mixture Transverse based rare R layer Glass-based layer rupture Rare earth earth magnet oxide R oxide Alloy R oxide Content of Br iHc BHmax Resistivity strength magnet layer layer particles phase particles glass layer (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 71 R—Fe—B-based Lu₂O₃ Lu₂O₃ R-rich Lu₂O₃ SiO₂—Al₂O₃—RrO 1.13 0.98 227 1350 165 invention rare earth phase Prior art magnet Lu₂O₃ 1.16 0.97 238 33 26 powder K Present 72 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ B₂O₃—ZnO 1.19 1.84 254 840 136 invention rare earth phase Prior art magnet Dy₂O₃ 1.21 1.83 259 30 34 powder L Present 73 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich Dy₂O₃ PbO—B₂O₃ 1.08 1.59 207 2980 205 invention rare earth phase Prior art magnet Dy₂O₃ 1.13 1.58 226 48 22 powder M Present 74 R—Fe—B-based Tb₂O₃ Tb₂O₃ R-rich Tb₂O₃ SiO₂—B₂O₃—PbO 1.07 1.48 204 2310 196 invention rare earth phase Prior art magnet Tb₂O₃ 1.12 1.47 223 45 20 powder N Present 75 R—Fe—B-based Gd₂O₃ Gd₂O₃ R-rich Gd₂O₃ Al₂O₃—B₂O₃—PbO 1.12 1.14 222 1430 176 invention rare earth phase Prior art magnet Gd₂O₃ 1.16 1.13 239 41 29 powder O

TABLE 17 High strength and high electrical resistance composite layer Composition R oxide particle- Properties of R—Fe—B- based mixture Transverse based rare R layer Glass-based layer rupture Rare earth earth magnet oxide R oxide Alloy R oxide Content of iHc BHmax Resistivity strength magnet layer layer particles phase particles glass layer Br (T) (MA/m³) (kJ/m³) (μΩm) (MPa) Present 76 R—Fe—B-based Dy₂O₃ Dy₂O₃ R-rich — SnO—P₂O₅ 1.11 1.54 220 1180 151 invention rare earth phase Prior art magnet Dy₂O₃ 1.15 1.52 236 37 26 powder P Present 77 R—Fe—B-based Pr₂O₃ Pr₂O₃ R-rich — ZnO—P₂O₅ 1.13 1.06 225 1950 184 invention rare earth phase Prior art magnet Pr₂O₃ 1.17 1.05 245 40 33 powder Q Present 78 R—Fe—B-based Y₂O₃ Y₂O₃ R-rich — ZnO—P₂O₅ 1.05 1.66 195 2780 189 invention rare earth phase Prior art magnet Y₂O₃ 1.10 1.65 214 44 26 powder R Present 79 R—Fe—B-based Er₂O₃ Er₂O₃ R-rich — CuO—P₂O₅ 1.08 1.51 206 2110 177 invention rare earth phase Prior art magnet Er₂O₃ 1.13 1.50 225 39 36 powder S Present 80 R—Fe—B-based Ho₂O₃ Ho₂O₃ R-rich — SiO₂—B₂O₃—ZnO 1.12 1.40 222 700 147 invention rare earth phase Prior art magnet Ho₂O₃ 1.16 1.39 238 33 32 powder T

From the results shown in Tables 14 through 17, it can be seen that the rare earth magnets 61 through 80 of the present invention have particularly higher strength and higher electrical resistance than the rare earth magnets 61 through 80 of the prior art.

Example 5

R—Fe—B-based rare earth magnet green compact layers having thickness of 3 mm were formed in a magnetic field from the R—Fe—B-based rare earth magnet powder A through T shown in Table 1.

Rare earth element oxide targets made from Dy₂O₃, Pr₂O₃, La₂O₃, Nd₂O₃, CeO₂, Tb₂O₃, Gd₂O₃, Pr₂O₃, Y₂O₃, Er₂O₃, and Sm₂O₃ were prepared. Sputtered layers of oxide having thickness of 5 μm were formed on the surface of the R—Fe—B-based rare earth magnet green compact layer by using the rare earth oxide target, thereby making the stacked body comprising the R—Fe—B-based rare earth magnet green compact layer and the R oxide layer.

The glass powders having compositions shown in Tables 18 through 21 with the average particle size of 2 μm were prepared. A plurality of the stacked bodies were stacked so as to provided the glass powder layer between the R oxide layers of the stacked bodies facing each other, thereby making a plurality of stacked green compacts each constituted from the R—Fe—B-based rare earth magnet green compact layer, R oxide layer, glass powder layer, R oxide layer, and the R—Fe—B-based rare earth magnet green compact layer. The stacked green compact was hot-pressed at a temperature of 750° C. under a pressure of 147 MPa, thereby making the rare earth magnets 81 through 100 of the present invention in the form of bulk measuring 10 mm in length, 10 mm in width, and 6.5 mm in height, comprising the high strength and high electrical resistance composite layer that was constituted from the R—Fe—B-based rare earth magnet layer having a composition shown in Tables 18 through 21, the R oxide layer having composition shown in Tables 18 through 21 and the glass layer having composition shown in Tables 18 through 21.

The rare earth magnets 81 through 100 of the present invention made as described above were polished on the top and bottom surfaces and four side faces thereof. A pair of voltage terminals were applied with a space of 4 mm from each other to the rare earth magnets 81 through 100 of the present invention that were polished, across one R—Fe—B-based rare earth magnet layer to the other R—Fe—B-based rare earth magnet layer of the side face that included the high strength and high electrical resistance composite layer while straddling the high strength and high electrical resistance composite layer. A pair of current terminals were applied with a space of 6 mm from each other so as to cross over the pair of voltage terminals. Resistance R=E/I (Ω) was calculated from the voltage drop E (V) across the voltage terminals when a predetermined current I (A) was flown between the current terminals, and resistance was calculated from the cross sectional area A (approximately 100 mm²) and the distance d between the terminals (=4 mm) by formula R×A/d, with the results shown in Tables 18 through 21. Remanence, coercivity and maximum energy product of the rare earth magnets 81 through 100 of the present invention were measured, with the results shown in Tables 18 through 21, then transverse rupture strength of the rare earth magnets 81 through 100 of the present invention were measured, with the results shown in Tables 18 through 21.

Comparative Example 5

A plurality of stacked bodies comprising the R—Fe—B-based rare earth magnet green compact layer and the R oxide layers made in Example 5 were stacked so that the R oxide layers of the stacked bodies face each other, thereby making a plurality of stacked green compacts each constituted from the R—Fe—B-based rare earth magnet powder green compact layer and the R oxide layers. The stacked green compact was hot-pressed at a temperature of 750° C. under a pressure of 147 MPa, thereby making the rare earth magnets 81 through 100 of the prior art in the form of bulk constituted from the R—Fe—B-based rare earth magnet layer having compositions shown in Tables 18 through 21 and the R oxide layer having compositions shown in Tables 18 through 21 stacked one on another, measuring 10 mm in length, 10 mm in width, and 6.5 mm in height.

The rare earth magnets 81 through 100 of the prior art made as described above were polished on the top and bottom surfaces and four side faces thereof A pair of voltage terminals were applied with a space of 4 mm from each other to the rare earth magnets 81 through 100 of the present invention that were polished, across one R—Fe—B-based rare earth magnet layer to the other R—Fe—B-based rare earth magnet layer of the side face that included the R oxide layer while straddling the R oxide layer. A pair of current terminals were applied with a space of 6 mm from each other so as to cross over the pair of voltage terminals. Resistance R=E/I (Ω) was calculated from the voltage drop E (V) across the voltage terminals when a predetermined current I (A) was flown between the current terminals, and resistance was calculated from the cross sectional area A (approximately 100 mm²) and the distance d between the terminals (=4 mm) by formula R×A/d, with the results shown in Tables 18 through 21.

Remanence, coercivity, and maximum energy product of the rare earth magnets 81 through 100 of the present invention were measured by the ordinary methods, with the results shown in Tables 18 through 21, then transverse rupture strength of the rare earth magnets 81 through 100 of the present invention were measured, with the results shown in Tables 18 through 21. Resistivity was measured by 4-probe method, with the results shown in Tables 18 through 21.

Remanence, coercivity and maximum energy product of the rare earth magnets 81 through 100 of the prior art were measured by the ordinary methods, with the results shown in Tables 18 through 21, then transverse rupture strength of the rare earth magnets 81 through 100 of the prior art were measured, with the results shown in Tables 18 through 21.

TABLE 18 Composition of High strength and high Properties R—Fe—B-based electrical resistance Transverse Rare earth rare earth magnet composite layer Br iHc BHmax Resistivity rupture strength magnet layer R oxide layer Glass layer (T) (MA/m³) (kJ/m³) (μΩm) (Mpa) Present 81 R—Fe—B-based Dy₂O₃ SiO₂—BaO—Al₂O₃ 1.19 1.54 251 345 120 invention rare earth magnet Prior art powder A — 1.19 1.52 251 38 24 Present 82 R—Fe—B-based Pr₂O₃ SiO₂—BaO—B₂O₃ 1.21 1.17 261 390 195 invention rare earth magnet Prior art powder B — 1.21 1.15 262 33 27 Present 83 R—Fe—B-based Ho₂O₃ SiO₂—BaO—Li₂O₃ 1.18 1.13 246 225 90 invention rare earth magnet Prior art powder C — 1.18 1.12 246 23 23 Present 84 R—Fe—B-based Dy₂O₃ SiO₂—MgO—Al₂O₃ 1.15 1.71 234 450 240 invention rare earth magnet Prior art powder D — 1.15 1.69 236 35 28 Present 85 R—Fe—B-based Nd₂O₃ SiO₂—ZnO—RrO 1.17 1.63 244 420 120 invention rare earth magnet Prior art powder E — 1.17 1.61 245 50 24

TABLE 19 Composition of High strength and high Properties R—Fe—B-based electrical resistance Transverse Rare earth rare earth magnet composite layer Br iHc BHmax Resistivity rupture strength magnet layer R oxide layer Glass layer (T) (MA/m³) (kJ/m³) (μΩm) (Mpa) Present 86 R—Fe—B-based Nd₂O₃ SiO₂—B₂O₃—ZnO 1.19 1.16 251 360 120 invention rare earth magnet Prior art powder F — 1.19 1.15 251 40 24 Present 87 R—Fe—B-based Lu₂O₃ SiO₂—Al₂O₃—RrO 1.17 0.98 245 330 180 invention rare earth magnet Prior art powder G — 1.18 0.97 246 25 26 Present 88 R—Fe—B-based Dy₂O₃ B₂O₃—ZnO 1.21 1.84 261 375 120 invention rare earth magnet Prior art powder H — 1.21 1.83 262 43 24 Present 89 R—Fe—B-based Dy₂O₃ PbO—B₂O₃ 1.17 1.59 244 435 90 invention rare earth magnet Prior art powder I — 1.17 1.58 245 58 23 Present 90 R—Fe—B-based Tb₂O₃ SiO₂—B₂O₃—PbO 1.16 1.48 240 405 120 invention rare earth magnet Prior art powder J — 1.16 1.47 241 48 24

TABLE 20 Composition of High strength and high Properties R—Fe—B-based electrical resistance Transverse Rare earth rare earth magnet composite layer Br iHc BHmax Resistivity rupture strength magnet layer R oxide layer Glass layer (T) (MA/m³) (kJ/m³) (μΩm) (Mpa) Present 91 R—Fe—B-based Gd₂O₃ Al₂O₃—B₂O₃—PbO 1.20 1.14 256 315 105 invention rare earth magnet Prior art powder K — 1.20 1.13 257 35 24 Present 92 R—Fe—B-based Dy₂O₃ SnO—P₂O₅ 1.19 1.54 251 300 150 invention rare earth magnet Prior art powder L — 1.19 1.52 252 25 25 Present 93 R—Fe—B-based Pr₂O₃ ZnO—P₂O₅ 1.21 1.06 262 360 135 invention rare earth magnet Prior art powder M — 1.21 1.05 262 38 25 Present 94 R—Fe—B-based Y₂O₃ ZnO—P₂O₅ 1.14 1.66 230 375 165 invention rare earth magnet Prior art powder N — 1.14 1.65 231 35 26 Present 95 R—Fe—B-based Er₂O₃ CuO—P₂O₅ 1.16 1.51 240 345 165 invention rare earth magnet Prior art powder O — 1.16 1.50 241 30 26

TABLE 20 Composition of High strength and high Properties R—Fe—B-based electrical resistance Transverse Rare earth rare earth magnet composite layer Br iHc BHmax Resistivity rupture strength magnet layer R oxide layer Glass layer (T) (MA/m³) (kJ/m³) (μΩm) (Mpa) Present 96 R—Fe—B-based Ho₂O₃ SiO₂—B₂O₃—ZnO 1.19 1.40 251 360 135 invention rare earth magnet Prior art powder P — 1.19 1.39 251 38 25 Present 97 R—Fe—B-based Dy₂O₃ SiO₂—B₂O₃—RrO 1.19 1.81 250 593 134 invention rare earth magnet Prior art powder Q — 1.19 1.79 251 21 23 Present 98 R—Fe—B-based Dy₂O₃ SiO₂—B₂O₃—ZnO 1.22 1.50 266 667 149 invention rare earth magnet Prior art powder R — 1.23 1.49 268 24 24 Present 99 R—Fe—B-based Dy₂O₃ SiO₂—B₂O₃—RrO 1.24 1.02 273 315 150 invention rare earth magnet Prior art powder S — 1.24 1.01 273 28 25 Present 100 R—Fe—B-based Dy₂O₃ SiO₂—B₂O₃—Al₂O₃ 1.16 1.50 240 450 180 invention rare earth magnet Prior art powder T — 1.16 1.48 241 45 26

From the results shown in Tables 18 through 21, it can be seen that the rare earth magnets 81 through 100 of the present invention have particularly higher strength and higher electrical resistance than the rare earth magnets 81 through 100 of the prior art.

Example 6

R oxide layer having thickness of 3 μm and compositions shown in Tables 22 through 25 were formed on the surfaces of the R—Fe—B-based rare earth magnet powders A through T having the average particle size of 300 μm that had been subjected to HDDR treatment shown in Table 1 by means of a powder coating sputtering apparatus, thereby to prepare oxide-coated R—Fe—B-based rare earth magnet powder.

The oxide-coated R—Fe—B-based rare earth magnet powder having the R oxide layer formed on the surface thereof was mixed with glass powders having compositions shown in Tables 22 through 25, all having the average particle size of 0.8 μm, and the mixed powder was formed preliminarily in a magnetic field under a pressure of 49 MPa and was then hot-pressed at a temperature of 730° C. under a pressure of 294 MPa, thereby making the rare earth magnets 101 through 120 of the present invention in the form of bulk measuring 10 mm in length, 10 mm in width, and 7 mm in height of a structure such that the R—Fe—B-based rare earth magnet particles having compositions shown in Tables 22 through 25 were enclosed with the high strength and high electrical resistance composite layer comprising the R oxide layer and the glass layer.

The rare earth magnets 101 through 120 of the present invention in the form of bulk made as described above were polished on the surfaces thereof, and resistivity was measured with the results shown in Tables 22 through 25.

Remanence, coercivity, and maximum energy product of the rare earth magnets 101 through 120 of the present invention were measured by the ordinary methods, with the results shown in Tables 22 through 25, then transverse rupture strength of the rare earth magnets 101 through 120 of the present invention were measured, with the results shown in Tables 22 through 25.

Comparative Example 6

The oxide-coated R—Fe—B-based rare earth magnet powder made in Example 6 having the R oxide layer 3 μm in thickness formed on the surface thereof was subjected to preliminary forming in a magnetic field under a pressure of 49 MPa and was then subjected to hot pressing at a temperature of 730° C. under a pressure of 294 MPa, thereby making the rare earth magnets 101 through 120 of the prior art in the form of bulk measuring 10 mm in length, 10 mm in width, and 7 mm in height having a structure such that the R—Fe—B-based rare earth magnet particles were enclosed with the R oxide layers.

The rare earth magnets 101 through 120 of the prior art in the form of bulk made as described above were polished on the surfaces thereof, and resistivity was measured with the results shown in Tables 22 through 25.

Remanence, coercivity, and maximum energy product of the rare earth magnets 101 through 120 of the prior art were measured by the ordinary methods, with the results shown in Tables 22 through 25, then transverse rupture strength of the rare earth magnets 101 through 120 of the prior art were measured, with the results shown in Tables 22 through 25.

TABLE 22 High strength and high Composition of electrical resistance Properties R—Fe—B-based composite layer Transverse Rare earth rare earth magnet R oxide Br iHc BHmax Resistivity rupture strength magnet layer layer Glass layer (T) (MA/m³) (kJ/m³) (μΩm) (Mpa) Present 101 R—Fe—B-based Dy₂O₃ SiO₂—BaO—Al₂O₃ 1.11 1.54 218 1125 222 invention rare earth magnet — 1.12 1.52 224 66 36 Prior art powder A Present 102 R—Fe—B-based Pr₂O₃ SiO₂—BaO—B₂O₃ 1.14 1.17 231 390 137 invention rare earth magnet — 1.15 1.15 235 63 27 Prior art powder B Present 103 R—Fe—B-based Ho₂O₃ SiO₂—BaO—Li₂O₃ 1.10 1.13 215 1065 87 invention rare earth magnet — 1.10 1.12 217 72 28 Prior art powder C Present 104 R—Fe—B-based Dy₂O₃ SiO₂—MgO—Al₂O₃ 0.97 1.71 171 825 196 invention rare earth magnet — 1.02 1.69 185 46 23 Prior art powder D Present 105 R—Fe—B-based Nd₂O₃ SiO₂—ZnO—RrO 1.10 1.63 214 735 146 invention rare earth magnet — 1.11 1.61 220 43 25 Prior art powder E

TABLE 23 High strength and high Composition of electrical resistance Properties R—Fe—B-based composite layer Transverse Rare earth rare earth magnet R oxide Br iHc BHmax Resistivity rupture strength magnet layer layer Glass layer (T) (MA/m³) (kJ/m³) (μΩm) (Mpa) Present 106 R—Fe—B-based Nd₂O₃ SiO₂—B₂O₃—ZnO 1.14 1.16 231 375 179 invention rare earth magnet Prior art powder F — 1.15 1.15 236 36 35 Present 107 R—Fe—B-based Lu₂O₃ SiO₂—Al₂O₃—RrO 1.15 0.98 234 660 220 invention rare earth magnet Prior art powder G — 1.16 0.97 238 33 26 Present 108 R—Fe—B-based Dy₂O₃ B₂O₃—ZnO 1.20 1.84 257 585 182 invention rare earth magnet Prior art powder H — 1.21 1.83 259 30 34 Present 109 R—Fe—B-based Dy₂O₃ PbO—B₂O₃ 1.11 1.59 221 840 187 invention rare earth magnet Prior art powder I — 1.13 1.58 226 48 22 Present 110 R—Fe—B-based Tb₂O₃ SiO₂—B₂O₃—PbO 1.10 1.48 217 810 204 invention rare earth magnet Prior art powder J — 1.12 1.47 223 45 20

TABLE 24 High strength and high Composition of electrical resistance Properties R—Fe—B-based composite layer Transverse Rare earth rare earth magnet R oxide Br iHc BHmax Resistivity rupture strength magnet layer layer Glass layer (T) (MA/m³) (kJ/m³) (μΩm) (Mpa) Present 111 R—Fe—B-based Gd₂O₃ Al₂O₃—B₂O₃—PbO 1.15 1.14 235 705 151 invention rare earth magnet Prior art powder K — 1.16 1.13 239 41 29 Present 112 R—Fe—B-based Dy₂O₃ SnO—P₂O₅ 1.14 1.54 232 645 137 invention rare earth magnet Prior art powder L — 1.15 1.52 236 37 26 Present 113 R—Fe—B-based Pr₂O₃ ZnO—P₂O₅ 1.16 1.06 238 750 214 invention rare earth magnet Prior art powder M — 1.17 1.05 245 40 33 Present 114 R—Fe—B-based Y₂O₃ ZnO—P₂O₅ 1.08 1.66 207 825 233 invention rare earth magnet Prior art powder N — 1.10 1.65 214 44 26 Present 115 R—Fe—B-based Er₂O₃ CuO—P₂O₅ 1.11 1.51 218 765 247 invention rare earth magnet Prior art powder O — 1.13 1.50 225 39 36

TABLE 25 High strength and high Composition of electrical resistance Properties R—Fe—B-based composite layer Transverse Rare earth rare earth magnet R oxide Br iHc BHmax Resistivity rupture strength magnet layer layer Glass layer (T) (MA/m³) (kJ/m³) (μΩm) (Mpa) Present 116 R—Fe—B-based Ho₂O₃ SiO₂—B₂O₃—ZnO 1.14 1.40 233 600 151 invention rare earth magnet Prior art powder P — 1.16 1.39 238 33 32 Present 117 R—Fe—B-based Dy₂O₃ SiO₂—B₂O₃—RrO 1.17 1.81 244 855 221 invention rare earth magnet Prior art powder Q — 1.18 1.79 246 47 38 Present 118 R—Fe—B-based Dy₂O₃ SiO₂—B₂O₃—ZnO 1.19 1.50 254 1005 249 invention rare earth magnet Prior art powder R — 1.20 1.49 257 56 21 Present 119 R—Fe—B-based Dy₂O₃ SiO₂—B₂O₃—RrO 1.20 1.02 255 555 121 invention rare earth magnet Prior art powder S — 1.21 1.01 259 32 25 Present 120 R—Fe—B-based Dy₂O₃ SiO₂—B₂O₃—Al₂O₃ 1.10 1.50 215 885 210 invention rare earth magnet Prior art powder T — 1.11 1.48 221 50 29

From the results shown in Tables 23 through 25, it can be seen that the rare earth magnets 101 through 120 of the present invention have particularly higher strength and higher electrical resistance than the rare earth magnets 101 through 120 of the prior art.

While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the spirit or scope of the present invention. Accordingly, the invention is not to be considered as being limited by the foregoing description, and is only limited by the scope of the appended claims. 

1. A rare earth magnet having a structure such that R—Fe—B-based rare earth magnet particles are enclosed within a composite layer, where R represents one or more kinds of rare earth element including Y, and wherein the composite layer comprises a glass-based layer having a glass phase or a structure of R oxide particles dispersed in a glass phase, and R oxide particle-based mixture layers that are formed on both sides of the glass-based layer and which contain an R-rich alloy phase containing 50 atomic % or more of R in a grain boundary of the R oxide particles.
 2. The rare earth magnet according to claim 1, wherein the composite layer further comprises an R oxide layer formed on the surface of the R oxide particle-based mixture layer opposite to the surface thereof that makes contact with the glass-based layer.
 3. The rare earth magnet according to claim 2, wherein R of the R oxide layer contained in the composite layer is one or more selected from the group consisting of Y, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
 4. The rare earth magnet according to claim 1, wherein the R—Fe—B-based rare earth magnet particles are particles of a rare earth magnet that have a composition such as 5 to 20 atomic % of R and 3 to 20 atomic % of B, with the balance consisting of Fe and inevitable impurities.
 5. The rare earth magnet according to claim 1, wherein the R—Fe—B-based rare earth magnet particles are particles of a composition such as 5 to 20 atomic % of R, 3 to 20 atomic % of B, and 0.001 to 5 atomic % of M, with the balance consisting of Fe and inevitable impurities, M represents one or more selected from the group consisting of Ga, Zr, Nb, Mo, Hf, Ta, W, Ni, Al, Ti, V, Cu, Cr, Ge, C, and Si.
 6. The rare earth magnet according to claim 1, wherein the R—Fe—B-based rare earth magnet particles have a composition such as 5 to 20 atomic % of R, 0.1 to 50 atomic % of Co, and 3 to 20 atomic % of B, with the balance consisting of Fe and inevitable impurities.
 7. The rare earth magnet according to claim 1, wherein the R—Fe—B-based rare earth magnet particles have a composition such as 5 to 20 atomic % of R, 0.1 to 50 atomic % of Co, 3 to 20 atomic % of B, and 0.001 to 5 atomic % of M, with the balance consisting of Fe and inevitable impurities, wherein M represents one or more selected from the group consisting of Ga, Zr, Nb, Mo, Hf, Ta, W, Ni, Al, Ti, V, Cu, Cr, Ge, C, and Si.
 8. The R—Fe—B-based rare earth magnet according to claim 1, wherein the R—Fe—B-based rare earth magnet particles are a magnetically anisotropic HDDR magnetic layer having a recrystallization texture comprising adjoining recrystallized grains containing an R₂Fe₁₄B type intermetallic compound phase of a substantially tetragonal structure as a main phase, while the recrystallization texture has a fundamental structure having a constitution such that 50 atomic % by volume or more of the recrystallized grains have a shape such that a ratio b/a of the minimum grain size a and the maximum grain size b of the recrystallized grains is less than 2, and the average size of the recrystallized grains is in a range from 0.05 to 5 μm. 